l 


THE   CENTURY   SCIENCE   SERIES 
EDITED   BY   SIR   HENRY   E.    ROSCOE,   D.C.L.,    F.R.S.,   LL.D. 


JUSTUS    VON    LIEBIG 


The  Century  Science  Series. 

EDITED    BY 

SIR  HENRY   E.   ROSCOE,  D.C.L.,  F.R.S.,  M.P. 


By   Ci 

of  the 


_  John  Dalton  and  the  Rise  of  Modern  Chemistry. 

By  Sir  HENRY  E.  ROSCOE,  F.R.S. 

Major  Eennell,  F.R.S.,  and  the  Rise  of  English 
Geography. 

CLEMENTS   R.    MARKHAM,  C.  B.,  F.R.S.,  President 
Royal  Geographical  Society. 

— •  Justus  von  Liebig :  his  Life  and  Work. 

By  W.  A.  SHENSTONE,  Science  Master  in  Clifton  College. 

The  Herschels  and  Modern  Astronomy. 

By   Miss  AGNES   M.  CLERKE,   Author   of   "A   Popul  ir 
History  of  Astronomy  during  the  igth  Century,"  £c. 
In  Preparation. 

...  Michael  Faraday:  his  Life  and  Work. 

By  Professor  SILVANUS  P.  THOMPSON,  F.R.S. 

Clerk  Maxwell  and  Modern  Physics. 

By  R.  T.  GLAZEBROOK,  F.R.S.,  Fellow  of  Trinity  College, 
Cambridge. 

Charles  Lyell :  his  Life  and  Work. 

By  Rev.  Professor  T.  G.  BONNEY,  F.R.S. 

-  Humphry  Davy. 

By    T.    E.   THORPE,    F.R.S.,    Principal   Chemist    of  the 
Government  Laboratories. 

—  Pasteur :  his  Life  and  Work. 

By  ARMAND  RUFFER,  Director  of  the  British  institute  of 
Preventive  Medicine. 

—  Charles  Darwin  and  the  Origin  of  Species. 

By  EDWARD  B.  POULTON,  M.A.,  F.R.S.,  Hope  Professor 
pf  Zoology  in  the  University  of  Oxford. 

—Hermann  von  Helmholtz. 

By  A.  W.  RUCKER,   F.R.S.,  Professor  of  Physics  in  the 
Royal  College  of  Science,  London. 
CASSELL  &  COMPANY,  LIMITED,  London;  P  ar  is  &>  Melbourne. 


Photo  by  Pram  ffanfstaengl,  Munich. 

JUSTUS    VON    LIEBIG. 

Born  May  12, 1803. 


Died  April  18, 1873. 


THE  CENTURY  SCIENCE  SERIES 

JUSTUS  VON  LlEBIG 

HIS   LIFE  AND  WORK 

(1803-1873) 


BY 

W.    A.    SHEISI STONE,    F.I.C. 

Lecturer  on  Chemistry  in  Clifton,  College 


MACMILLAN     &     CO. 

1902 


PREFACE. 


THE  name  of  Liebig  is  doubtless  familiar  to  most  of 
us,  but  I  fear  that  very  few  have  any  clear  idea  what 
he  did,  why  chemists  admire  and  esteem  him,  or, 
indeed,  are  aware  that  they  do  admire  and  esteem 
him.  As  the  result  of  many  inquiries,  made  among 
cultivated  people,  I  have  found  the  prevailing  im- 
pression concerning  Liebig  to  be  that  he  was  a  man 
who  gained  a  large  fortune  by  making  "extract  of 
meat."  Now  and  then  one  meets  someone  who  "seems 
to  have  heard  "  of  his  name  in  connection  with  agri- 
culture. Scarcely  anyone,  now,  seems  to  know  that 
he  was  one  of  the  greatest  of  that  class  in  whose  work 
Mr.  Balfour  finds  "  the  causes  which,  more  than  any 
others,  conduce  to  the  movements  of  great  civilised 
societies."  I  have  therefore  made  it  my  object,  in 
writing  this  little  book,  not  so  much  to  dwell  upon 
Liebig's  private  life  as  to  tell  what  he  was,  what 
he  did,  and  why  all  chemists  and  aU  those  who  are 
versed  in  the  history  of  science  admire  and  esteem 
him  so  greatly. 

Fortunately  for  my  purpose,  most  of  Liebig's  work 
is  not  only  of  great  general  interest,  but  it  lends  itself 
admirably  to  a  non-technical  method  of  treatment. 
Consequently,  I  have  only  found  it  necessary  to 
employ  the  language  of  chemistry  in  parts  of  two 
chapters.  As  I  have  been  careful  to  explain  technical 
terms  when  I  have  used  them,  and  as  I  have  not  very 


Univ,  Library,  UC  Santa  Cruz  199>0 

vi  PREFACE. 

often  employed  them,  I  do  not  think  they  will  be  a 
real  source  of  difficulty  or  repel  anyone. 

If  any  chemist  should  read  this  life  of  Liobig,  he 
may  not  improbably  feel  disposed  to  complain  that 
it  does  something  less  than  justice  to  Liebig's  labours 
in  pure  chemistry.  I  admit  that  this  is  very  true. 
But  it  is  right  that  it  should  be  so,  for,  vast  as 
were  Liebig's  services  to  pure  chemistry,  they  lack  in 
some  degree  the  splendour  of  his  contributions  to 
some  other  departments  of  equal  intrinsic  importance 
and  of  far  wider  general  interest. 

In  concluding  these  few  introductory  words,  I 
desire  to  express  my  thanks  to  several  very  kind 
helpers :  to  Liebig's  son,  Dr.  Georg  Baron  Liebig,  who 
has  assisted  me  most  graciously  in  several  ways ;  to 
my  friend  and  colleague,  H.  Clissold,  who  has  most 
carefully  read  the  proofs  for  me;  and  to  my  wife, 
who  has  very  materially  lightened  my  task  by  helping 
me  to  go  through  the  greater  part  of  the  numerous 
bulky  volumes  which  contain  Liebig's  published 
correspondence. 

W.   A.   S. 

Clifton,  May,  181)5. 


CONTENTS. 


PAGE 


CHAPTER    I.— INTRODUCTION 

„          II.— LlEBIG   AND    WOHLER 

III.— CHEMICAL  DISCOVERIES 
IV.— LIEUIG  AND  DUMAS 

V. FERMENTATION 

VI.— CHEMISTRY  OF  AGRICULTURE 
VII.—  PHYSIOLOGICAL  CHEMISTRY  . 

„  VIII.— EDUCATIONAL  AND  OTHER  WORK         .  173 

IX.— CHARACTER  AND  LATER  YEARS    .  19" 


JUSTUS    VON   LlEBIG: 

HIS     LIFE     AND     WORK. 


CHAPTER  I. 

Introduction— Early  Life  and  Tastes — His  "Wander- Year — Appoint- 
ment at  Giessen — Method  of  Organic  Analysis — Some  other 
Contributions  to  Chemical  Method. 

IT  is  remarkable  that  in  spite  of  the  epoch-making 
character  of  Liebig's  contributions  to  chemistry,  to 
agriculture,  to  physiology,  and  to  the  advancement 
of  education,  and  in  spite  of  the  fact  that  his  name 
is  still  a  household  word  over  a  large  part  of  two 
continents,  no  comprehensive  or  popular  account  of 
his  life  and  work  has  yet  been  written,  though  it  is 
more  than  twenty  years  since  death  robbed  us  of  one 
of  the  greatest  men  of  this  or  perhaps  of  any  other 
century. 

Of  Faraday — who  lived  and  worked  like  Liebig, 
one  might  almost  say  with  Liebig,  when,  to  men  of 
science,  the  times  were  young — we  have  already  two 
lives,  those  of  Dr.  Bence  Jones  and  of  Dr.  Gladstone. 
Of  Pasteur,  Liebig's  great  opponent  on  the  question 
of  the  cause  of  fermentation,  whose  personality 
stands  out  to-day  only  less  distinctly  than  did  that 
of  Liebig  fifty  years  ago,  we  have  a  delightful,  if 
rather  one-sided,  account  written  by  his  son-in-law, 
M.  Valery  Radot.  But  of  Liebig,  perhaps  the  greatest 
and  the  most  many-sided  of  all,  we  have  as  yet 


10  JUSTUS   VON   LIEBIG: 

only  the  memorial  addresses  of  August  Vogel  on 
his  work  in  agricultural  chemistry,  of  Emil  Erlen- 
meyer  on  his  contributions  to  pure  chemistry,  and 
of  Theodor  L.  W.  von  Bischoff  on  his  work  and  in- 
fluence on  physiology,  together  with  the  celebrated 
Faraday  lecture  of  his  brilliant  and  distinguished 
pupil  A.  W.  Hofmann,  some  too  brief  fragments  of 
autobiography,  Moriz  Carriere's  account  of  his  friend- 
ship with  Platen  the  poet,  and  some  more  fugitive 
but  still  interesting  contributions,  such  as  Sir  Henry 
Roscoe's  obituary  notice  in  Nature  of  May  8th,  1873. 

But  this  apparent  neglect  is  only  apparent,  and 
is  easy  to  understand.  Liebig,  owing  to  his  un- 
rivalled gift  of  popular  exposition,  was  his  own 
prophet.  As  he  had  no  need  of  an  interpreter 
while  he  lived,  so  there  was  no  immediate  need  of 
a  monument  after  his  death.  His  memorable 
"  Familiar  Letters  on  Chemistry,"  by  means  of 
which  he  conveyed  his  teachings  to  the  people, 
informed  those  of  his  own  and  the  succeeding 
generation  what  his  life-work  had  been  ;  and  they 
remained  as  a  sufficient  memorial  of  him  for  many 
years  after  he  was  gone. 

But  with  the  progress  of  science  the  time  has 
now  come,  as  it  was  sure  to  come,  when  the  majority 
of  readers  can  no  longer  safely  betake  themselves  to 
Liebig's  own  writings,  in  order  to  learn  the  part  he 
played  in  the  development  of  human  knowledge.  And 
it  is  a  question  whether  the  immense  value  of  his 
services  is  not  already  more  than  half  forgotten  owing 
to  the  absence  of  any  suitable  review  of  his  Avork. 
This  is  especially  true  of  his  educational  work.  How 
many  educated  men  of  to-day — nay,  how  many  of  the 
younger  chemists — are  aware  that  it  may  fairly  be 


HIS   LIFE   AND   WORK.  11 

said  that  it  was  he  who  paved  the  way  for  the  edu- 
cational revolution  which  will  be  for  long  associated 
with  the  second  half  of  the  nineteenth  century  by 
establishing  in  1825  at  Giessen  his  famous  labora- 
tory for  giving  instruction  to  all  comers  in  practical 
chemistry  ? 

Justus  von  Liebig  was  born  on  May  12th,  1803,  at 
Darmstadt,  where  his  father  dealt  in  colours,  which 
he  also  frequently  manufactured  according  to  the  pro- 
cesses then  prescribed  in  works  on  chemistry,  some- 
times with  the  aid  of  his  small  son.  As  a  schoolboy, 
Liebig  was  not  a  success  from  the  pedagogic  point 
of  view ;  his  bent  of  mind  was  so  distinctly  that  of 
the  experimenter  that,  as  he  tells  us,  his  position  at 
school  was  very  deplorable.  Like  many  other  lads  of 
this  type,  he  had  no  ear  memory,  and  could  retain 
little  or  nothing  of  what  he  learned  through  the  sense 
of  hearing,  with  the  result  that  he  found  himself  in 
as  uncomfortable  a  position  as  a  boy  could  possibly 
occupy.  Not  only  were  all  the  acquirements  that  led 
to  praise  and  honour  in  the  school  utterly  out  of  his 
reach,  but  once  the  good  Rector  of  the  gymnasium,  on 
the  occasion  of  examining  Liebig's  class,  made  a  most 
cutting  and  public  remonstrance  with  him,  reproached 
him  for  want  of  diligence,  told  him  he  was  the 
plague  of  his  teachers  and  the  sorrow  of  his  parents, 
and  ended  by  asking  him  what  did  he  think  was  to 
become  of  him.  Liebig,  who,  though  so  ignorant  in 
the  linguistic  studies  of  the  place,  was  already  pretty 
widely  read  in  science  and  versed  in  the  operations  of 
chemistry,  replied,  amid  the  uncontrollable  laughter 
of  the  good  rector  and  of  the  whole  school,  "  That  he 
would  be  a  chemist."  No  one  at  that  time  had  any 


12  JUSTUS   VON  LIEBIG  : 

idea  that  chemistry  was  a  subject  that  could  be 
studied  for  itself.  To  most  it  was  a  mere  accessory 
subject,  at  best  a  handmaid  to  medicine  and  phar- 
macy ;  the  idea  of  the  study  of  chemistry  being- 
adopted  as  a  career  seemed  preposterous.* 

It  was  plain,  however,  that  none  of  the  ordinary 
careers  open  to  a  gymnasium  student  were  possible 
for  Liebig,  and  owing,  doubtless,  to  his  inclination  for 
chemistry,  he  was  taken  by  his  father  to  an  apothecary 
at  Heppenheim.  Here  he  soon  became  acquainted 
with  the  various  applications  of  the  multifarious  con- 
tents of  a  druggist's  shop,  but  pill-making  did  not 
please  him  ;  he  wished  to  be  a  chemist,  not  a  druggist. 
Soon,  therefore,  he  began  to  make  experiments  of  a 
non-pharmaceutical  character  privately  in  his  attic  ; 
before  long,  accidents  occurred,  and  at  last  one  day 
the  attic  window-sash  was  blown  out.  At  the  end  of 
ten  months,  the  alarmed  apothecary  of  Heppenheim 
was  so  sorry  with  his  bargain  that  he  sent  the  lad 
home  again  to  his  father. 

Liebig  was  now  about  sixteen,  at  which  age  in 
those  days  most  lads  were  beginning  to  take  life 
seriously,  and  it  was  plainly  difficult  to  know  what  to 
do  with  him,  or  to  foresee  what  he  would  do  for  him- 
self. His  time  had  not,  however,  really  been  wasted. 
The  interest  he  had  taken  in  his  father's  work  had  led 
him  long  before  he  left  school  to  read  with  passionate 
interest  the  books  used  for  guidance  in  the  manu- 

*  The  above  and  many  other  personal  details  concerning  Liebig1  s 
early  life  are  taken,  frequently  in  his  own  words,  from  an  auto- 
biographical fragment,  which  was  discovered  by  his  son,  Dr.  Georg 
Baron  von  Liebig,  a  few  years  ago,  and  published  in  the  Deutsche 
Rundschau  for  January,  1891.  A  translation  of  this  sketch,  by  Prof. 
J.  Campbell  Brown,  was  read  at  Liverpool  on  March  19th  in  the  same 
year,  and  published  in  the  Chemical  News  on  June  5th  and  12th. 


HIS   LIFE    AND   WORK.  13 

facture  of  colours.  In  fetching  these  books  from  the 
Court  Library  he  had  become  acquainted  with  the 
Librarian,  Hess,  through  whose  kindness  he  soon 
had  the  run  of  the  library,  where  he  read  in  anyhow 
fashion  such  works  as  Macquer  on  Chemistry ;  Basil 
Valentine's  Triumphal  Car  of  Antimony ;  Stahl's 
Phlogistic  Theory ;  together  with  numerous  essays 
and  treatises,  including  the  writings  of  Kir  wan  and 
Cavendish.  0£  course,  as  he  tells  us,  he  did  not  in 
this  way  gain  much  exact  knowledge  from  his  reading, 
but  it  led  him  to  attempt  to  carry  out  the  experiments 
which  he  read  about  as  far  as  his  means  would  allow, 
and,  these  being  very  limited,  to  make  countless 
repetitions  of  such  of  them  as  he  was  able  to  perform, 
with  the  result  that,  boy  as  he  was,  he  had  already 
acquired,  in  a  considerable  degree,  that  power  of 
perceiving  the  resemblances  and  differences  between 
things  and  between  phenomena  which  he  has  called 
sight-  or  eye-memory. 

Every  one  of  the  numerous  white  precipitates 
known  to  the  chemist  has  some  quality  or  qualities 
peculiar  to  itself  which  should  be  recognised  by  those 
who  have  once  fully  studied  it.  Liebig's  early  habit 
of  experimenting  helped  to  develop  in  him  the  eye- 
memory  which  makes  this  possible.  This  power  was 
afterwards  possessed  by  him  to  such  an  extent  that  in 
later  years  he  was  sometimes  able  to  recognise,  by  their 
appearances  alone,  eleven  rare  chemicals  many  years 
after  having  once  worked  with  them,  with  such  cer- 
tainty that  he  was  not  even  misled  by  the  results 
of  the  analysis  of  impure  specimens. 

Though  Liebig  had  not  mastered  the  lessons  of  the 
gymnasium,  he  had  gained  a  knowledge  of  most  of  the 
processes  carried  on  in  his  neighbourhood.  He  had 


14  JUSTUS   VON   LIEBIG: 

watched  the  soap-boiler,  and  had  made  soap  on  his  own 
account.  "  In  the  workshop  of  the  tanner  and  dyer, 
the  smith  and  brass  founder,  he  was  at  home  and 
ready  to  do  any  hand's  turn."  Nay,  as  we  shall  see, 
he  had  even  drawn  inspiration  from  a  peripatetic 
cheapjack  who  visited  Darmstadt,  and  plied  his  trade 
in  the  market  place,  as  he  watched  him  prepare  ful- 
minating silver  for  his  pea- crackers,  and  clean  coat 
collars  for  the  country  folk.  Left  to  himself,  he  had 
gained  extensive  stores  of  information,  and  a  deep- 
seated  desire  for  more,  and  at  the  age  of  sixteen,  by 
persistent  importunity,  he  induced  his  father  to  per- 
mit him  to  go  to  the  University  of  Bonn,  whence  he 
afterwards  followed  his  professor,  Kastner,  to  Erlangen 
on  the  removal  of  the  latter  to  that  university. 

There  had  arisen,  Liebig  tells  us,  about  that  time 
at  the  then  newly-established  University  of  Bonn,  an 
extraordinary  quickening  of  scientific  life,  which,  how- 
ever, was  unfortunately  most  perniciously  affected  by 
the  philosophical  methods  of  investigation  as  they  had 
been  embodied  by  Oken  and  by  Wilbrand,  which  had 
led  alike  in  lecture  and  in  study  to  a  want  of  appre- 
ciation of  experiment  and  of  an  unprejudiced  obser- 
vation of  nature  that  was  ruinous  to  many  talented 
young  men — "  From  the  professorial  chair  the  pupils 
received  an  abundance  of  ingenious  contemplations ; 
but,  bodiless  as  they  were,  nothing  could  be  made 
of  them." 

At  this  time  Sir  Humphry  Davy  and  others  in 
England ;  Berzelius,  the  great  Swede ;  and  in  France 
a  whole  galaxy  of  brilliant  experimenters,  includ- 
ing Gay-Lussac,  Dulong,  Arago,  and  Chevreul,  were 
rapidly  opening  out  new  spheres  of  investigation  of 
almost  boundless  importance,  but  their  inestimable 


HIS  LIFE   AND  WORK.  15 

acquisitions  found  no  soil,  and  could  bear  no  fruit 
in  Germany,  where,  as  Liebig  says,  "  It  was  then  a 
wretched  time  for  chemistry." 

At  Bonn  and  Erlangeftftherefore,  Liebig  soon  learnt 
that  he  was  not  in  the  way  to  become  a  chemist. 
But  here  he  also  discovered,  from  his  intercourse  with 
other  students,  his  own  ignorance  of  many  subjects 
with  which  they  had  gained  an  acquaintance  at  school. 
This  was  something,  and  since  he  could  learn  no 
chemistry,  he  exerted  all  his  energies  to  make  up 
for  his  previously  neglected  school  studies  ;  whilst  by 
organising  and  working  with  a  small  band  of  students, 
who  formed  themselves  into  a  cheinico-physical  union, 
he  gained  some  practice  in  composition  and  in  the 
art  of  speaking.  But  this  was  all,  and  before  long  he 
returned  to  Darmstadt,  persuaded  that  he  could  not 
become  a  chemist  in  Germany. 

Up  to  this  time  Liebig's  career  had  certainly  been 
calculated  to  give  a  good  deal  of  anxiety  to  his  rela- 
tions, especially  as  latterly  he  had  come  into  conflict 
with  the  authorities,  and  was  even  at  one  time  under 
arrest  for  supposed  political  offences,  though  he  was 
not,  as  we  are  told  by  Platen,  conscious  of  any  real 
fault  of  his  own.  But  there  is  no  doubt  that  even  at 
this  early  stage  he  showed,  to  those  who  were  capable 
of  judging  him,  an  extraordinary  degree  of  promise. 
He  had  not  only  attracted  the  interest  of  Hess,  but 
he  was  the  favourite  pupil  of  Kastner  the  chemist, 
whilst  the  poet  Platen  may  almost  be  said  to 
have  fallen  in  love  with  him  at  sight.  The  latter 
wrote  of  him  in  his  diary  on  March  13th,  1822 : — 
"  The  day  before  yesterday  I  made  an  interesting 
acquaintance.  This  is  a  young  chemist  from  Darm- 
stadt, who  is  named  Justus  Liebig,  the  same  student 

l*^\&u^^ 


16  JUSTUS  VON   LIEBIG: 

whom  I  met  some  time  since  at  Kastner's.  Billow  had 
already  described  him  to  me  as  Kastner's  favourite,  as  he 
has,  particularly  in  chemistry,  very  sound  knowledge." 
Before  long  Platen  and  Liebig  met  again,  walked 
in  the  country,  and  afterwards  adjourned  to  Liebig's 
dwelling-place.  Platen  afterwards  declared  his  new 
friend  to  be  clear,  definite,  and  solid  in  everything, 
and,  above  all,  on  the  side  of  the  affections,  open  and 
confiding.  "Never  before,"  said  he,  "have  I  been  treated 
with  such  affection  upon  so  brief  an  acquaintance." 
Owing  to  various  accidents,  the  meetings  of  these  two 
were  very  few,  but  Platen  has  left  us  a  delightful 
description  of  Liebig's  personality  at  this  period. 
"  Liebig,"  he  said,  writing  after  a  walk  with  him,  "  was 
never  more  beautiful.  Of  slender  form,  a  friendly 
earnestness  in  his  regular  features,  great  brown  eyes 
with  dark  shady  eyebrows,  which  attracted  one  in- 
stantly  Oh  that  I  might,  after  so  many 

deceptions,  find  happiness  and  peace  in  this  friendship, 
which  seems  to  open  up  new  future  possibilities ! " 

In  1822,  at  the  age  of  nineteen,  Liebig  took  the 
degree  of  Doctor  of  Philosophy  at  Erlangen,  and  at 
about  the  same  time  he  published  the  result  of  his 
first  attempt  at  an  investigation  in  a  paper  on  the 
composition  of  fulminating  mercury,  which  was 
remarkable  for  the  clearness  and  precision  of  its 
language.  This  paper  and  some  analyses  of  certain 
colouring  matters  which  he  had  also  already  performed 
fortunately  attracted  the  attention  of  people  who  pos- 
sessed influence  with  Louis  the  First,  the  then  reign- 
ing Grand  Duke  of  Hesse-Darmstadt.  Before  long 
Liebig's  chance  came.  He  had  the  good  fortune  to  be 
provided  by  Duke  Louis  with  the  necessary  means  for 
prosecuting  his  studies  abroad. 


HIS   LIFE   AND   WORK.  17 

But  whither  should  he  go  ? 

In  those  early  years  of  the  nineteenth  century  the 
younger  men  among  the  German  chemists  had  already 
many  of  them  repaired  to  Stockholm  in  search  of 
inspiration  and  instruction  in  the  modest  laboratory 
of  Berzelius.  Mitscherlich,  the  discoverer  of  iso- 
morphism; H.  Rose,  the  analyst;  and,  later  on,  Wohler, 
whose  production  of  urea  from  materials  of  purely  in- 
organic origin  afterwards  revolutionised  the  views  of 
chemists  on  organic  chemistry,  and  finally  established 
the  idea  of  isomerism  in  the  science — ah*  visited 
Sweden  to  become  the  pupils  and  friends  of  the  great 
Northern  chemist,  and  it  is  probable  that  Liebig,  to 
whom  the  writings  of  Berzelius  had  already  been  "  as 
springs  in  the  desert,"  would  have  followed  their 
footsteps  had  not  Paris  offered  him  opportunities  of 
wider  study  that  were  an  irresistible  attraction. 
Therefore,  to  Paris  he  went,  to  sit  at  the  feet  of  the 
great  masters  who  adorned  the  French  capital  at  that 
time.  There  he  found  the  opportunities  he  desired. 
The  lectures  consisted  of  a  wisely-arranged  succession 
of  experiments,  whose  connection  was  completed  by 
oral  explanations.  "  The  experiments,"  says  Liebig,  in 
his  autobiographic  fragment,  "  were  a  real  delight  to 
me,  for  they  spoke  to  me  in  a  language  I  understood, 
and  they  united  with  the  lecture  in  giving  a  definite 
connection  to  the  mass  of  shapeless  facts  which  lay 
mixed  up  in  my  head  without  order  and  without 
arrangement,"  whilst  the  lectures,  as  a  whole,  made  a 
most  marked  impression  on  his  mind  by  their  intrinsic 
truth,  by  the  absence  of  pretence. 

At  the  time  of  Liebig's  arrival  in  France — that  is 
to  say,  in  1822 — there  did  not  exist  in  all  Paris  nor  in 
all  the  world  one  such  public  laboratory  for  workers 


18  JUSTUS   VON   LIEBIG: 

in  chemistry  or  physics  as  may  now  be  found  in 
every  provincial  town  of  the  first  class.  Though  the 
lectures  were  so  excellent,  public  places  of  instruction 
in  analysis  and  experimenting  generally  were  still  as 
completely  non-existent  in  France  as  in  Germany, 
and  admittance  into  a  chemical  laboratory  was  then 
a  difficult  thing  indeed  for  a  stranger  to  attain.  By 
the  kind  assistance  of  Thenard,  however,  Liebig  was 
permitted  to  continue  his  researches  on  explosives  in 
the  private  laboratory  of  Gaultier  de  Claubry,  and  he 
soon  published  another  paper  on  this  subject.  But  he 
was  not  even  then  able  to  feel  complete  confidence 
in  his  results,  and  he  was  meditating  yet  further  ex- 
periments, when  by  a  happy  chance,  in  the  summer 
of  1823,  he  made  the  acquaintance  of  Humboldt 
the  traveller.  From  that  day  Liebig  found  all  doors 
and  all  laboratories  open  to  him  as  by  magic,  and  he 
was  soon  at  work  in  the  laboratory  of  Gay-Lussac, 
revising  his  analyses  of  the  fulminates,  with  the  result 
that  early  in  the  next  year  he  brought  them  to  a 
successful  conclusion,  and  was  rewarded  by  the  dis- 
covery of  isomerism  and  by  the  honour  of  a  waltz 
round  the  laboratory  with  his  distinguished  teacher, 
who  was  in  the  habit  of  relieving  his  feelings,  as 
he  explained  to  his  young  friend,  when  discoveries 
were  made,  by  such-like  terpsichorean  exercises. 

The  account  of  Liebig's  meeting  with  Humboldt, 
and  of  his  introduction  to  Gay-Lussac,  was  told  by 
him  years  afterwards  to  Mr.  E.  K.  Muspratt  in  the 
Munich  Laboratory,  and  is  so  interesting  that  it 
deserves  to  be  repeated. 

One  day  in  the  summer  of  1823  he  gave 
an  account  of  his  earlier  analyses  of  fulminating 
silver  before  the  Academy  of  Sciences.  Having 


HIS   LIFE   AND  WORK.  19 

finished  his  paper,  as  he  was  packing  up  his  pre- 
parations a  gentleman  caine  up  to  him  and  ques- 
tioned him  as  to  his  studies  and  future  plans,  and, 
after  an  exacting  examination,  ended  by  asking  him 
to  dinner  on  the  following  Sunday.  Liebig  accepted 
the  invitation,  but,  through  nervousness  and  con- 
fusion, forgot  to  ask  the  name  and  address  of  his 
interviewer.  Sunday  came,  and  poor  Liebig  was  in 
despair  at  not  being  able  to  keep  his  engagement. 

The  next  day  a  friend  came  to  him  and  said, 
"  What  on  earth  did  you  mean  by  not  coming  to  dine 
with  von  Humboldt  yesterday,  who  had  invited  Gay- 
Lussac  and  other  chemists  to  meet  you  ?  "  "I  was 
thunderstruck,"  said  Liebig.  "  I  rushed  off  as  fast 
as  I  could  run  to  von  Humboldt's  lodgings,  and  made 
the  best  excuses  I  could."  The  great  traveller,  satis- 
fied with  the  explanation,  told  him  it  was  unfortu- 
nate, as  he  had  several  members  of  the  Academy  at 
his  house  to  meet  him,  but  thought  he  could  make 
it  all  right  if  he  would  come  to  dinner  next  Sunday. 
He  went,  and  then  made  the  acquaintance  of  Gay- 
Lussac,  who  was  so  struck  with  the  genius  and 
enthusiasm  of  the  youth  that  he  took  him  into  his 
private  laboratory,  and  continued  in  conjunction  with 
him  the  investigation  of  the  fulminating  compounds. 

Nor  did  Humboldt's  assistance  stop  here,  for  it  was 
on  his  recommendation  that  Liebig  was  afterwards 
appointed  Professor  in  the  little  University  of  Giessen, 
where  he  established  a  school,  whose  achievements 
in  pure  and  applied  chemistry  must  have  far  tran- 
scended the  most  sanguine  of  his  youthful  aspirations. 
From  the  most  modest  beginning  and  the  scantiest 
means  came  results  which  fill  one  of  the  most 
splendid  pages  in  the  history  of  chemistry.  It  was 


20  JUSTUS   VON   LIEBIG  : 

in  Gay-Lussac's  laboratory  that  Liebig,  conscious 
of  what  he  owed  to  the  guidance  and  friendship 
of  his  master,  and  conscious  too  of  his  own  growing 
insight  and  power,  conceived  the  idea  of  founding 
in  Germany  a  school  where  he  should  be  to  his 
younger  fellow  workers  that  which  Gay-Lussac  had 
been  to  himself.  A  glorious  dream  gloriously  ful- 
filled, as  we  shall  presently  see. 

Liebig  was  appointed  Extraordinary  Professor  of 
Chemistry  at  Giessen  in  1824,  and  Ordinary  Pro- 
fessor two  years  later.  He  was  called  to  Munich  in 
1852,  and  died  there  on  April  18th,  1873. 

Liebig  was  essentially  a  pioneer  in  science.  In 
the  course  of  his  life  he  took  the  lead  in  no  less 
than  four  great  departures.  The  first  was  in  organic 
chemistry,  the  second  and  third  in  the  applications 
of  chemistry  to  agriculture  and  to  physiology,  the 
fourth,  as  will  presently  appear,  was  the  outcome  of 
his  labours  as  a  teacher.  His  work,  like  that  of  other 
pioneers,  was,  of  course,  not  always  correct  in  all 
points  of  detail.  But  it  had  all  the  greater  merits 
of  good  pioneering  work  in  a  most  marked  degree. 
It  almost  always  pointed  the  right  way,  and  its  re- 
markable influence  in  determining  the  direction  of 
subsequent  research  has  been  singularly  permanent. 

But  a  pioneer  in  science,  like  a  traveller,  must  not 
set  out  till  he  is  fully  equipped.  It  was  useless  for 
Liebig  or  anyone  else  to  attempt  to  explore  the  depths 
of  organic  chemistry  before  a  method  for  the  analysis 
of  organic  substances  was  at  his  command.  This 
Liebig  knew  full  well,  and  accordingly  we  find  that 
his  leisure  during  his  first  years  at  Giessen  was 
devoted  to  contriving  such  a  method. 

When   the   chemist  discovers   a  new   substance, 


HIS  LIFE   AND   WORK.  21 

whatever  its  nature  may  be,  whether  it  is  composed 
of  the  so-called  mineral  elements,  such  as  the  metals, 
sulphur,  phosphorus,  chlorine,  etc.,  or  whether  it 
belongs  to  the  so-called  organic  group  of  compounds 
in  which  the  presence  of  carbon,  oxygen,  hydrogen, 
nitrogen,  are  especially  characteristic,  it  is  necessary 
in  the  first  place  to  learn  its  ultimate  composition — 
that  is  to  say,  to  find  out  by  analysis  what  elements 
it  contains,  and  in  what  exact  proportions  they  are 
present. 

In  organic  analysis  the  chemist  has  usually  only 
to  deal  with  some  eight  or  ten  elements,  and  often 
with  only  three  or  four — viz.  with  compounds  of 
carbon,  with  hydrogen,  oxygen,  or  nitrogen;  hence 
the  operations  of  ultimate  organic  analysis  are 
characterised  by  their  comparative  simplicity ;  but 
success  in  this  branch  of  work  has  only  been  attained 
as  the  result  of  many  failures,  owing  to  the  great 
initial  difficulties  whiph  for  half  a  century  prevented 
chemists  from  making  much  progress. 

Lavoisier  was  one  of  the  first  to  attempt  to  analyse 
organic  compounds.  He  knew  that  carbon,  when 
burnt,  yields  the  well-known  heavy,  suffocating  car- 
bonic acid  gas,  and  he  had  established,  with  some 
approach  to  precision,  the  relative  proportions  in 
which  carbon  and  oxygen  enter  into  its  composition. 

Similarly  from  the  work  of  Cavendish,  and  from 
his  own  experiments,  Lavoisier  knew  approximately  the 
relative  proportions  in  which  hydrogen  and  oxygen 
unite  to  form  water.  Armed  with  these  three  facts, 
he  endeavoured  to  ascertain  the  proportions  in  which 
carbon,  hydrogen,  and  oxygen  are  present  in  alcohol 
and  oil,  by  burning  weighed  quantities  of  them  in  small 
lamps  placed  under  receivers,  standing  over  mercury,  to 


22  JUSTUS  VON  LIEBIG: 

which  such  additional  measured  volumes  of  oxygen  as 
might  be  necessary  could  be  added  during  the  process. 
At  the  end  of  the  process  he  measured  the  carbonic 
acid  gas  formed,  and  the  volume  of  the  air  which 
remained.  From  the  data  so  obtained  he  endeavoured 
to  calculate  the  composition  of  the  substance  burnt  in 
his  lamp ;  but,  unfortunately,  neither  his  knowledge  of 
the  composition  of  the  compounds  produced,  nor  of 
the  relative  densities  of  the  gases  concerned,  was 
sufficiently  accurate  for  his  purpose,  and  hence  the 
results  of  his  experiments  had  no  permanent  value. 
Later  he  made  other  experiments,  in  which  he  collected 
and  weighed  the  products  of  burning  oil,  but  these 
were  cut  short  by  his  pseudo-judicial  murder  in  1794. 
It  was  not  until  Liebig  attempted  to  solve  the 
problem  that  success  was  really  attained ;  and  Liebig 
only  achieved  complete  success  after  devoting  many 
years  to  thinking  and  experimenting. 

The  method  of  organic  analysis  given  to  chemistry 
by  Liebig,  like  that  of  Lavoisier,  consists  in  completely 
burning,  or  oxidising,  the  substance  which  is  to  be 
analysed,  and  then  collecting  and  measuring  the  car- 
bonic acid  gas  and  water  formed.  This  process  is  at  once 
admirable  in  its  conception  and  in  its  execution.  It 
is  a  model  of  simplicity  and  accuracy.  It  remains 
in  use,  almost  unchanged,  to  this  day ;  it  has  served 
for  the  analysis  of  countless  numbers  of  organic  sub- 
stances, and  has  thus  formed  the  very  foundation  on 
which  the  whole  vast  structure  of  modern  organic 
chemistry  is  based.  It  may  fairly  be  said  to  be  one  of 
Liebig's  greatest  gifts  to  science.  The  details  of  this 
beautiful  process  cannot  be  here  described,  but  may 
be  found  in  every  treatise  on  organic  chemistry.  In 
contriving  it,  Liebig  selected  with  unerring  judgment 


HIS  LIFE  AND  WORK.  23 

all  that  was  best  in  the  ideas  of  his  predecessors ; 
added  his  famous  absorption  apparatus,  "Liebig's 
potash  bulbs;"  and  embodied  the  whole  in  a  form 
which  remains  nearly  intact  after  half  a  century. 

Modifications  of  Liebig's  process  that  were  suitable 
for  bodies  containing  other  elements,  such  as  nitrogen, 
chlorine,  and  sulphur  were  soon  introduced,  some  of 
them  by  Liebig  or  his  pupils,  and  thus  the  fundamental 
difficulty  which  had  retarded  the  progress  of  organic 
chemistry  to  an  almost  inconceivable  extent  for 
nearly  fifty  years  was  overcome,  and  Liebig  and  his 
pupils  were  able  to  carry  out  the  numerous  investiga- 
tions which  have  given  the  little  Hessian  University  a 
world- wide  reputation. 

By  the  analysis  of  a  compound,  however,  the 
chemist  only  learns  the  relative  proportions  in  which 
its  constituents  have  combined  to  form  it.  Analysis 
alone  tells  him  nothing  about  the  weight  of  its 
molecule  (page  32) ;  and  until  he  knows  this,  as  well 
as  the  percentage  composition  of  a  substance,  he  can 
neither  tell  in  what  numbers  the  atoms  of  its 
component  elements  occur  in  its  molecules,  nor 
proceed  to  the  important  work  of  investigating  its 
constitution — that  is  to  say,  the  relations  of  these 
various  atoms  to  one  another. 

The  methods  of  weighing  molecules  are,  some  of 
them  physical,  some  of  them  chemical  Liebig  made 
important  contributions  to  the  latter  class,  by  teaching 
us  two  elegant  processes,  suitable  for  the  group  of 
compounds  known  as  the  organic  bases.  The  first 
is  no  longer  much  in  use,  but  its  successor,  which 
consists  in  the  analysis  of  the  compounds  they  form 
with  chloride  of  platinum,  is  still  frequently  used,  and 
is  highly  valued  for  its  accuracy. 


24  JUSTUS  VON  LIEBIG  : 

In  concluding  this  brief  sketch  of  some  of  Liebig's 
chief  contributions  to  chemical  method,  all  of  which 
were  characterised  by  simplicity,  elegance,  and  ac- 
curacy, one  cannot  refrain  from  alluding  first  to  the 
process  of  gas  analysis,  in  which  he  employed  the 
long-known  power  of  alkaline  solutions  of  pyrogallic 
acid  to  absorb  oxygen,  for  the  purpose  of  measuring 
the  volume  of  that  gas  in  air  and  other  gaseous  mixtures 
containing  it,  and  also  took  advantage  of  the  necessary 
use  of  potash  in  this  process  to  combine  the  measure- 
ment of  oxygen  with  that  of  carbonic  acid  gas.  And, 
secondly,  to  the  "  Liebig's  Condenser."  This,  however, 
will  be  already  familiar  to  nearly  every  one  who  has 
visited  a  chemical  laboratory.  No  single  instrument 
has  done  better  service  to  experimental  chemistry 
than  this.  It  is,  as  we  all  know,  in  daily  and  hourly 
use  in  every  laboratory.  It  has  become  almost  as 
essential  to  the  work  of  every  student  of  chemistry  as 
the  test-tube. 


HIS  LIFE   AND   WORK.  25 


CHAPTER  II. 

LIEBIG   AND   WOHLER. 

Liebig  and  Wohler — Wdhler's  Early  Life — His  Visit  to  Berzelius — 
The  Composition  of  Fulminic  Acid  and  Cyanic  Acid — Isomerism 
— Liebig  and  Wohler  meet  —They  Propose  to  Work  Together — 
Researches  on  Oil  of  Bitter  Almonds — The  Benzoyl  Theory — 
Study  of  Uric  Acid  and  its  Derivatives — The  Characters  of  Liebig 
and  Wohler  Contrasted— Their  Mutual  Esteem. 

IT  would  be  impossible  to  tell  the  story  of  Liebig  and 
his  work  without  soon  referring  to  his  joint  labours 
and  life-long  intimacy  with  Friedrich  Wohler.  Their 
joint  work  and  their  friendship  will  be  remembered, 
and  will  link  the  names  of  Liebig  and  Wohler  through 
all  time  in  the  mind  of  every  student  of  chemistry, 
equally  for  the  purity  and  warmth  which  charac- 
terised their  historic  alliance,  and  for  the  epoch- 
making  results  which  were  the  outcome  of  their 
mutual  endeavours. 

Friedrich  Wohler  was  born  in  the  neighbourhood 
of  Frankfort  on  the  31st  of  July,  1800.  Like  Liebig, 
he  showed  at  an  early  age  a  passion  for  experiment- 
ing, which  is  said  to  have  been  the  cause  of  frequent 
neglect  of  his  studies  at  the  gymnasium.  His  scientific 
tastes  were  fostered  and  directed  by  Dr.  Buch,  a 
physician  who  sympathised  with  his  inclinations,  and 
who  had  himself  devoted  time  to  the  study  of 
chemistry  and  physics.  His  father,  who  was  a  citizen 
of  some  position  in  Frankfort,  on  the  other  hand, 
encouraged  in  him  a  taste  for  drawing,  for  the  litera- 
ture of  his  country,  and,  above  all,  indoctrinated  him 
with  a  love  of  outdoor  life  and  exercise,  which  was 


26  JUSTUS   VON   LIEBIG: 

probably  in  a  great  degree  the  cause  of  the  almost 
constant  good  health*  that  he  enjoyed  throughout  a 
long  and  active  life. 

After  obtaining  his  degree  in  1823,  a  year  later 
than  Liebig,  Wohler  determined,  on  the  advice  of 
Gmelin,  to  place  himself  under  the  direction  of 
Berzelius,  at  Stockholm,  who  was  then  at  the  summit 
of  his  fame  alike  on  account  of  his  achievements  in 
analysis  and  for  his  contributions  to  chemical  theory ; 
and  Berzelius  having  been  applied  to,  and  having 
consented  to  his  desire,  Wohler  was  soon  on  his  way 
to  the  famous  laboratory  in  Sweden.  The  following 
account  of  his  reception,  and  of  the  laboratory  and 
life  at  Stockholm,  will  be  interesting  to  everyone  who 
has  visited  a  laboratory  of  to-day  : — "  With  a  beating 
heart,"  he  says,  "I  stood  before  Berzelius's  door  and  rang 
the  bell.  It  was  opened  by  a  vigorous  and  portly  man. 
This  was  Berzelius  himself.  As  he  led  me  into  his 
laboratory  I  was  as  in  a  dream,  doubting  if  I  could 
really  be  in  the  classical  place  which  was  the  object 
of  my  aspirations.  ...  I  was  then  the  only  one 
in  the  laboratory.  .  .  .  The  laboratory  consisted 
of  two  ordinary  rooms,  furnished  in  the  simplest 
possible  way ;  there  were  no  furnaces  or  draught 
places,  neither  gas  nor  water  supply.  In  one  of  the 
rooms  were  two  common  deal  tables ;  at  one  of  these 
Berzelius  worked,  the  other  was  intended  for  me. 
On  the  walls  were  a  few  cupboards  for  reagents ;  in 
the  middle  was  a  mercury  trough,  whilst  the  glass 
blower's  lamp  stood  on  the  hearth.  In  addition  was 
a  sink  with  an  earthenware  cistern  and  tap  standing 
over  a  wooden  tub,  where  the  despotic  Anna,  the  cook, 
had  daily  to  clean  the  apparatus.  In  the  other  room 
were  the  balances,  and  some  cupboards  containing 


HIS  LIFE  AND  WORK.  27 

instruments ;  close  by  was  a  small  workshop  fitted 
with  a  lathe." 

"  In  the  adjacent  kitchen,  in  which  Anna  prepared 
the  meals,  Avas  a  small  and  seldom  used  furnace  and  a 
never  cool  sand-bath."  Anna  appears  to  have  picked 
up  the  elements  of  nomenclature,  for  Wohler  tells 
us  that  he  was  not  a  little  surprised  on  one  occasion 
to  hear  Berzelius  chide  her  for  saying  that  some 
apparatus  she  was  cleaning  smelt  strongly  of  oxy- 
muriatic  acid,  saying,  "  Hearest  thou,  Anna,  thou 
must  no  longer  speak  of  oxymuriatic  acid  ;  thou  must 
call  it  chlorine ;  that  is  better." 

After  a  year  at  Stockholm,  Wohler's  visit  to 
Berzelius  was  brought  to  a  conclusion  by  a  short 
period  of  travel  in  Southern  Sweden  and  Norway, 
which  was  partly  devoted  to  collecting  geological 
specimens  and  partly  to  sport.  In  the  course  of  his 
travels  he  met  Davy,  who,  like  Wohler,  had  a  marked 
taste  for  active  outdoor  exercises. 

This  tour  completed,  Wohler  returned  to  Germany, 
having  contracted  a  friendship  with  Berzelius  which 
continued  without  interruption  throughout  the  life  of 
the  latter,  in  spite  of  the  fact  that  Wohler's  subsequent 
work  with  Liebig  brought  him  into  occasional  conflict 
with  the  rather  tightly  held  convictions  of  Berzelius 
on  various  points  of  chemical  theory. 

After  his  return  to  Germany,  Wohler  accepted  a 
post  at  the  then  recently  founded  trade  school  in 
Berlin,  and  thus  obtained  possession  of  a  laboratory 
of  his  own ;  he  stayed  in  Berlin  about  six  years,  and 
during  this  period,  besides  less  important  work,  he 
succeeded  for  the  first  time  in  isolating  aluminium 
by  a  process  which  has  only  lately  been  superseded ; 
and  accomplished  the  transformation  of  ammonium 


28  JUSTUS   VON   LIEBIG: 

cyanate,  an  inorganic  substance,  into  urea,  one  of  the 
most  characteristic  of  animal  products,  thereby  break- 
ing down  the  imaginary  barrier  between  the  products 
of  the  chemical  and  the  so-called  vital  forces,  and 
opening  out  a  new  field  of  investigation  which  is  still 
inexhausted,  and  seems  inexhaustible. 

Above  all,  during  these  years  he  found  Liebig. 
The  mode  in  which  they  were  brought  together  is 
one  of  the  romances  of  science.  Whilst  still  a  boy, 
Liebig's  attention  had  been  drawn  to  the  fulminates, 
a  class  of  bodies  which  owe  their  name  to  their 
violently  explosive  character,  when  watching  a  peri- 
patetic dealer  in  odds-and-ends  make  fulminating 
silver  for  fire-crackers  in  the  market-place  at  Darm- 
stadt, by  dissolving  silver  in  nitric  acid,  and  then 
adding  a  liquid  which  smelt  of  brandy — with  which 
he  also  cleaned  dirty  coat  collars  for  the  rustics — 
to  the  product.  Liebig's  attention  was  so  strongly 
drawn  to  this  body,  that  he  afterwards,  as  has  already 
been  mentioned,  made  repeated  examinations  and 
analyses  of  it,  which  were  only  brought  to  a  success- 
ful issue  by  the  work  done  in  Gay-Lussac's  laboratory 
in  1823-24. 

At  almost  the  same  time  Wohler  was  occupied 
with  his  investigations  of  another  and  very  dissimilar 
substance,  cyanic  acid,  in  the  laboratory  of  Berzelius. 
When  Liebig  had  finally  satisfied  himself  as  to  the 
composition  of  fulminic  acid,  he  was  surprised  to 
find  that  his  results  coincided  with  the  analyses  of 
cyanic  acid  made  and  published  by  Wohler  somewhat 
earlier. 

Cyanic  acid  and  fulminic  acid  were  so  obviously 
different  that  no  one  could  confuse  them.  Such 
a  result,  therefore,  seemed  almost  absurdly  impossible. 


HIS   LIFE   AND   WORK.  29 

How  could  the  same  elements  combine  in  the  same 
proportions  to  form  dissimilar  compounds  ?  It  was 
contrary  to  the  fundamental  principles  of  chemistry ; 
there  must  be  a  mistake  somewhere. 

Confident  that  his  own  results  were  correct,  Liebig 
repeated  the  investigation  of  Wohler.  But  this  was 
found  to  be  correct  too.  These  two  compounds,  so 
different  from  each  other,  were  indeed  identical  in 
their  composition. 

Berzelius  and  some  other  chemists  did  not  at 
first  accept  these  concluions,  in  spite  of  the  fact 
that  some  compounds  were  already  known  among 
inorganic  bodies,  which  were  opposed  to  the  axiom 
that  substances  having  the  same  qualitative  and 
quantitative  composition  must  exhibit  the  same 
properties.  But  Gay-Lussac  not  only  accepted  the 
results,  but  pointed  out  that  the  new  facts  might  be 
accounted  for  by  assuming  a  difference  in  the  manner 
in  which  the  constituent  elements  are  combined  in  the 
two  substances.  And  before  very  long  it  became 
impossible  for  any  one  to  doubt  the  existence  of  the 
phenomenon  of  isomerism,  as  it  was  named  by 
Berzelius,  which  was  thus  first  recognised  through 
the  work  of  these  two — Liebig  and  Wohler.  On  the 
very  threshold  of  their  careers,  these  two  men  had 
made  a  discovery  of  the  first  order.  It  w^as  inevitable 
that  they  should  become  rivals  or  friends.  It  was 
characteristic  of  them  that  they  became  friends.  Not 
indeed  at  once,  but  as  soon  as  an  opportunity  offered 
itself.  They  met,  some  time  after,  in  the  house  of  a 
common  friend  at  Frankfort,  and  the  acquaintance 
then  formed  soon  ripened  into  friendship,  and  resulted 
in  a  frequent  and  free  intercourse,  never  afterwards 
interrupted.  Their  friendship  was  soon  cemented  by 


30  JUSTUS  VON   LIEBIG: 

their  undertaking  the  joint  labours  which  have  in- 
separably united  their  names  in  the  annals  of  science. 

The  proposal  that  they  should  thus  join  hands 
came  first  from  Wohler,  in  the  following  characteristic 
letter : — 

"  SACROW,  near  POTSDAM,  8th  June,  1829. 

"DEAR  PROFESSOR, — The  contents  of  your  last  letter  to 
Poggendorff  have  been  communicated  to  me  by  him,  and  I  am 
glad  that  they  afford  me  an  opportunity  of  resuming  the 
correspondence  which  we  began  last  winter.  It  must  surely  be 
some  wicked  demon  that  again  and  again  imperceptibly  brings 
us  into  collision  by  means  of  our  work,  and  tries  to  make  the 
chemical  public  believe  that  we  purposely  seek  these  apples  of 
discord  as  opponents.  But  I  think  he  is  not  going  to  succeed. 
If  you  are  so  minded,  we  might,  for  the  humour  of  it,  undertake 
some  chemical  work  together,  in  order  that  the  result  might  be 
made  known  under  our  joint  names.  Of  course,  you  would 
work  in  Giessen  and  I  in  Berlin,  when  we  are  agreed  upon  the 
plan,  and  we  could  communicate  with  each  other  from  time  to 
time  as  to  its  progress.  I  leave  the  choice  of  subject  entirely 
to  you. 

"  I  am  very  glad  that  you  have  also  determined  the  identity 
of  pyro-uric  and  cyanic  acids.  Grnelin  would  say : — '  God  be 
thanked,  there  is  one  acid  the  loss.'  .  .  . — Yours, 

"  WOHLER." 

Liebig  expressed  his  joyful  assent  to  this  proposition 
at  once,  and  a  research  upon  mellitic  acid — the  acid 
of  honeystone — was  selected,  and  carried  to  a  success- 
ful issue.  Soon  after  publishing  their  results  they 
again  joined  forces,  at  Wohler's  suggestion,  to  make 
an  investigation  of  an  acid,  cyanuric  acid,  obtained 
by  him  from  urea,  in  the  course  of  which  Wohler 
observed  the  remarkable  examples  of  molecular 
re-arrangement,  which  occur  in  the  spontaneous 
transformation  of  the  liquid  cyanic  acid  into  its  iso- 
meride,  the  solid  cyanuric  acid,  and  the  re-conversion 
of  the  latter,  on  distillation,  into  cyanic  acid  once 


HIS   LIFE   AND   WORK.  31 

more.  It  was  next  proposed  that  fulminic  acid 
should  form  the  subject  of  a  new  and  joint  attack ; 
indeed,  Liebig  evidently  at  one  time  commenced 
operations.  These,  however,  were  soon  abandoned, 
for  he  wrote  on  November  18th,  1830  : — "  The  fulminic 
acid  we  will  allow  to  remain  undisturbed.  Like  you, 
I  have  vowed  to  have  nothing  more  to  do  with  this 
stuff.  Some  time  back  I  wanted,  in  connection  with 
our  work,  to  decompose  some  fulminating  silver  by 
means  of  ammonium  sulphide;  at  the  moment  the 
first  drop  fell  into  the  dish,  the  mass  exploded  under 
my  nose.  I  was  thrown  backwards,  and  was  deaf  for 
a  fortnight,  and  became  almost  blind." 

It  would  be  impossible  and  unfitting  in  this  book 
to  enter  at  any  length  into  the  details  of  the  fifteen 
memoirs  published  jointly  by  Wohler  and  Liebig,  but 
the  results  of  several  of  their  researches  are  of  such 
remarkable  importance,  and  have  played  so  great  a 
part  in  the  growth  of  chemistry,  that  it  is  impossible 
not  to  refer  to  some  of  them. 

First  in  importance  stands  their  research  on  oil 
of  bitter  almonds,  concerning  which  Berzelius  wrote 
to  them  : — "  The  facts  put  forward  by  you  give  rise 
to  such  considerations  that  they  may  well  be  deemed 
the  beginning  of  a  new  day  in  vegetal  chemistry." 

Well  might  Berzelius  commend  this  splendid  piece 
of  work.  It  was  one  of  the  most  prolific  of  their  joint 
investigations.  It  not  only  gave  several  new  and  im- 
portant compounds  to  chemistry,  but  it  also  exercised 
a  most  important  influence  on  the  growth  of  chemical 
theory,  by  establishing  in  organic  chemistry  the  con- 
ception of  what  are  called  compound  radicles. 

When  these  pioneers  in  the  new  organic  chemistry 
took  the  field,  in  1832,  oil  of  bitter  almonds  was 


32  JUSTUS   VON   LIEBIG: 

already  known  as  a  volatile  liquid  rendered  familiar  by 
its  characteristic  smell,  and  remarkable  for  its  power 
when  exposed  to  the  air  of  absorbing  oxygen  and 
changing  into  a  beautifully  crystalline  substance, 
then  as  now  known  as  benzole  acid. 

Armed  with  Liebig's  method  of  organic  analysis, 
the  two  chemists  soon  ascertained  the  true  com- 
position of  these  substances.  They  arrived  at  the 
formulae  by  which,  in  effect,  we  still  represent  them, 
and  made  the  exact  relation  of  the  one  to  the  other 
easy  to  understand. 

For  the  sake  of  those  of  my  readers  who  are  not 
acquainted  with  chemistry,  I  must  here  explain  that, 
according  to  the  conceptions  of  chemists,  the  larger 
masses  of  matter  with  which  we  are  familiar  may 
be  supposed  to  be  built  up  of  exceedingly  small 
and  indestructible  particles,  called  atoms.  These 
atoms  are  so  exceedingly  small  as  to  be  quite  beyond 
our  powers  of  seeing,  even  when  we  are  assisted 
by  the  most  powerful  microscopes.  The  atoms  of 
a  given  chemical  element  are  supposed  to  be  in 
every  way  identical  in  their  properties,  including 
their  weight.  Those  of  different  elements,  however, 
are,  on  the  other  hand,  unlike  in  their  properties. 
Atoms  are  supposed  to  be  endowed  with  the  power 
of  attracting  one  another  in  varying  degrees,  to 
form  the  molecules  of  compounds  or  of  elements. 

Chemists  are  in  the  habit  of  representing  these 
atoms  by  means  of  conventional  symbols.  Thus  the 
letter  H  represents  one  atom  of  hydrogen ;  0  one 
atom  of  oxygen ;  C  one  atom  o'f  carbon ;  N  one  atom 
of  nitrogen ;  Cl  one  atom  of  chlorine ;  and  so  on. 

Compounds  are  represented  by  placing  the  sym- 
bols of  the  combined  elements  close  to  each  other. 


HIS  LIFE  AND  WORK.  33 

Thus,  there  being  good  reason  to  conclude  that  each 
molecule  of  water  contains  two  atoms  of  hydrogen 
united  with  one  atom  of  oxygen,  we  give  the  formula 
HoO  to  this  substance. 

The  theory  thus  briefly  sketched  is  known  as 
the  "  Atomic  Theory."  We  owe  it  to  an  Englishman 
—John  Dalton,  of  Manchester.* 

When  Liebig  and  Wohler  had  worked  out  the 
formulae  of  oil  of  bitter  almonds  and  of  benzoic  acid, 
they  found  that  the  former  might  be  looked  upon  as 
a  compound  of  an  atom  of  hydrogen  with  a  group  of 
atoms,  or  radicle,  C-ELO,  which  we  call  benzoyl — i.e. 
as  C-ELO,  H ;  and  that  the  latter  might  be  considered 
to  contain  the  same  radicle  united  with  another 
group  or  radicle,  hydroxyl.  This  view  is  represented 
by  the  following  formulae,  in  which  benzoyl.  C7H5O, 
is  common  to  both  substances  : — 

OH  of  bitter  almonds  ...  ...     C7H5O,  H 

Benzoic  acid         ...  ...  ...     C7H5O,  OH 

By  other  experiments  they  discovered  several  more 
new  substances  which  might  also  be  regarded  as  com- 
pounds of  benzoyl.  These  are  given  in  the  following 
table ;  they  show  well  what  a  clearness  of  ideas  was 
gained  by  conceiving  the  presence  in  all  these  com- 
pounds of  a  common  group  of  atoms,  which  could 
be  transferred  from  one  compound  to  another,  as  it 
were,  like  a  single  atom  : —  C  Rr 

Oil  of  bitter  almonds  ...  ...  C7H50,  H 

Benzoic  acid          ...  ...  ...  C7H3O.(OH) 

„       chloride C7H50',  Cl 

„       bromide   ... '          ...  ...  C7H5O,  Br 

„       iodide       ...  ...  ...  C7H5O,  I 

„       cyanide    ...  ...  ...  C7H50,  CN 

*  Sec  "  John  Dalton  and  the  Rise  of  Modern  Chemistry  "  in  this 
series. 

C 


34  JUSTUS   VON   LIEBIG: 

This  idea  of  compound  radicles  was  not,  it  is  true, 
entirely  new  when  Liebig  and  Wohler  applied  it  in 
the  above  case,  for  Berzelius  had,  as  early  as  in  1820, 
attempted  to  compare  the  constitutions  of  organic 
substances  with  those  of  inorganic  compounds  by  the 
use  of  such  a  conception,  whilst  it  was  known  from 
the  researches  of  Gay-Lussac  that  cyanogen,  a  com- 
pound of  nitrogen  and  carbon,  acts  very  much  like 
an  element. 

But  a  real  appreciation  of  the  existence  of  a  con- 
nection between  the  properties  of  substances  and  the 
radicles  they  contain  was  mainly  brought  about,  in 
the  first  instance,  by  this  memorable  research  "  upon 
the  radicle  of  benzoic  acid." 

Well  might  these  investigators  modestly  congratu- 
late themselves  on  this  achievement.  They  had 
discovered  a  true  path  into  the  almost  unknown 
regions  of  organic  chemistry  by  their  "  Benzoyl 
Theory." 

But  Liebig  and  Wohler  did  not  stay  their  hands  at 
this  point.  It  was  known  that  oil  of  bitter  almonds 
does  not  exist  ready  formed  in  the  almonds  them- 
selves, and  that  the  almonds  contain  a  beautifully- 
crystalline  substance — amygdalin. 

In  1836  Wohler  was  selected  to  succeed  Stromeyer 
as  Professor  of  Chemistry  at  Gottingen.  The  choice  lay 
between  Liebig  and  Wohler  on  this  occasion.  As  soon  as 
he  was  ready  for  fresh  work,  he  wrote  to  Liebig  :—  "  I 
am  like  a  hen  which  has  laid  an  egg  and  straightway 
sets  up  a  great  cackling.  I  have  this  morning  found 
how  bitter  oil  of  almonds  containing  prussic  acid  may 
be  obtained  from  amygdalin,  and  would  propose  that 
we  jointly  undertake  the  further  investigation  of  the 
matter,  as  it  is  intimately  related  to  the  benzoyl 


HIS  LIFE   AND  WORK.  35 

research."  A  few  days  later  lie  wrote  that  he  had  made 
a  remarkable  discovery  in  relation  to  ainygdalin. 
Bitter  almond  oil  can  be  obtained  from  ainygdalin 
and  also  from  almonds,  and  it  occurred  to  him  that 
the  oil  might  be  produced  from  the  ainygdalin  by 
an  action  similar  to  that  of  a  ferment.  Experiments 
showed  that  this  hypothesis  was  well  borne  out  by  the 
facts,  for  he  found  that  an  emulsion  of  sweet  almonds 
which  contain  no  arnygdalin,  causes  the  formation  oi 
the  oil  and  of  prussic  acid,  when  it  acts  upon 
amygdalin.  From  this  they  inferred  the  presence 
both  in  bitter  and  sweet  almonds  of  a  "kind  of  soluble 
ferment,"  to  which  they  gave  the  name  emulsin.  Nor 
was  this  all.  From  their  analyses  of  amygdalin,  and 
of  oil  of  bitter  almonds  and  prussic  acid,  they  satisfied 
themselves  that  in  the  transformation  of  the  former 
something  besides  the  oil  and  prussic  acid  must  be 
produced;  something  had  been  missed.  They  soon 
discovered  this  complementary  product.  It  was  sugar. 
And  thus  they  made  known  to  chemistry,  for  the  first 
time,  a  member  of  another  new  and  most  important 
and  interesting  group  of  substances — viz.  the  glucos- 
ides,  and  at  the  same  time  made  an  important  contri- 
bution to  our  knowledge  of  ferments. 

The  joint  work  of  Liebig  and  Wohler  was  continued 
till  1838,  when  their  grand  investigation  of  uric  acid 
was  published.  Their  experiments  soon  showed  that 
the  interest  of  uric  acid  to  the  chemist  is  hardly 
interior  to  that  which  this  substance  excites  in  the 
physiologist.  The  readiness  with  which  it  takes  part 
hi  chemical  change  is  such  that,  in  a  single  research, 
they  added  no  less  than  sixteen  new  and  most  remark- 
able substances  to  the  list  of  organic  compounds, 
concerning  which  it  is  notable  that  in  the  course  of 


36  JUSTUS   VON   LIEBIG: 

nearly  half  a  century  only  one  of  them  disappeared 
from  the  science.  On  this  occasion,  as  on  that  of 
their  work  on  oil  of  bitter  almonds,  their  memoir 
was  not  only  remarkable  for  the  number  of  the 
new  substances  which  it  introduced  into  chemistry, 
it  was  again  distinguished  both  by  the  masterly 
interpretation  of  their  results,  in  which  they  again 
made  use  of  their  conception  of  organic  radicles,  and 
by  the  prescience,  which  enabled  them  to  foresee  the 
direction  in  which  organic  chemistry  was  about  to 
advance.  From  these  researches,  they  said: — "The 
philosophy  of  chemistry  must  draw  the  conclusion 
that  the  synthesis  of  all  organic  compounds  which 
are  not  organised  must  be  looked  upon  not  merely  as 
probable,  but  as  certain  of  ultimate  achievement. 
Sugar,  salicin,  morphine  will  be  artificially  prepared. 
As  yet,  we  are  ignorant  of  the  road  by  which  this  end 
will  be  reached,  since  the  proximate  constituents 
required  for  building  up  these  substances  are  not 
yet  known  to  us;  but  these  the  progress  of  science 
cannot  fail  to  reveal."  This  was  the  last  great  re- 
search undertaken  by  these  two  friends.  Liebig  soon 
afterwards  turned  his  attention  to  the  problems 
of  agricultural  and  physiological  chemistry,  whilst 
Wohler  thereafter  devoted  himself  chiefly  to  inorganic 
chemistry. 

It  is  natural,  nay  inevitable,  that  reference  should 
be  made  to  the  human  side  of  the  friendship  between 
these  two  men,  whose  names  are  so  entwined  with 
one  another  and  with  the  history  of  chemistry. 
Hofmann,  the  pupil  of  Liebig  and  the  editor  of  their 
correspondence,  has  left  us  a  picture  of  the  men  in 
which  each  figure  stands  clearly  before  us — "  Liebig, 
fiery  and  rash,  seizing  a  new  idea  with  enthusiasm, 


HIS    LIFE    AND    WORK.  37 

readily  giving  free  rein  to  his  imagination,  tenacious 
of  his  opinions,  yet  open  to  the  recognition  of  error, 
sincerely  grateful,  indeed,  to  those  who  made  him 
conscious  of  it.  Wohler,  calm  and  deliberate,  ap- 
proaching a  new  problem  with  temperate  considera- 
tion securely  guarded  against  over-hasty  conclusions ; 
but  both  equally  inspired  by  the  same  invariable 
love  of  truth.  Liebig,  irritable,  easily  offended,  hot- 
tempered,  hardly  master  of  his  emotions,  which  often 
found  vent  in  bitter  words  that  involved  him  in 
long  and  painful  quarrels.  Wohler,  unimpassioned, 
even  under  the  most  malignant  provocation,  disarm- 
ing the  bitterest  opponent  by  the  sobriety  of  his 
speech,  the  sworn  foe  of  quarrels  and  dissension,  yet 
both  animated  by  the  same  unerring  sense  of  right." 
Can  we  wonder  that  between  two  such  natures,  so 
different  and  yet  so  complementary,  there  should 
ripen  a  friendship  that  they  might  count  among  the 
best  harvests  of  their  lives.  The  following  letter 
from  Wohler,  on  the  occasion  of  one  of  Liebig's  fits  of 
annoyance,  indicates  the  manner  in  which  Wohler's 
influence  was  exerted  on  Liebig : — 

"  GOTTINGEN  March  9th,  1843. 

"  To  make  war  against  Marchand,  or,  indeed,  against,  anybody 
else,  brings  no  contentment  with  it  and  is  of  little  use  to  science. 
.  .  .  Imagine  that  it  is  the  year  1900,  when  we  are  both 
dissolved  into  carbonic  acid,  water,  and  ammonia,  and  onr  ashes, 
it  may  be,  are  part  of  the  bones  of  some  dog  that  has  despoiled 
onr  graves.  Who  cares  then  whether  we  have  lived  in  peace  or 
anger ;  who  thinks  then  of  thy  polemics,  of  the  sacrifice  of  thy 
health  and  peace  of  mind  for  science  ?  Nobody.  But  thy  good 
ideas,  the  new  facts  which  thou  hast  discovered — these,  sifted 
from  all  that  is  immaterial,  will  l)e  known  and  remembered  to 
all  time.  But  how  comes  it  that  I  should  advise  the  lion  to 
eat  sugar  ?  " 


38  JUSTUS  VON  LIEBIG: 

Nor  was  this  the  only  occasion  on  which  Wohler 
sought  to  moderate  the  occasional  in  temperance,  under 
provocation,  of  his  friend.  Thus  in  a  letter  of 
March  3rd,  1834,  on  the  occasion  of  another  dispute, 
he  warns  his  friend  that  he  may  be  right  and  may 
be  doing  a  service  to  knowledge,  but  that  he  em- 
bitters his  life  and  ruins  his  health  for  nothing. 

On  the  other  hand,  it  was  to  Liebig  and  Giessen 
that  Wohler  turned  when,  in  1832,  he  lost  his  young 
wife,  and  it  was  by  working  in  Liebig's  company  that 
he  sought  for  consolation  and  forgetfulness  after 
his  loss.  On  which  occasion  he  wrote  after  his 
return  to  Cassel — "  I  am  here  back  again  in  my 
darkened  solitude  .  .  .  How  happy  was  I  that 
we  could  work  together  face  to  face." 

And  again  on  another  occasion  he  wrote : — "  The 
days  which  I  spend  with  Liebig  slip  by  like  hours, 
and  I  count  them  among  my  happiest." 

As  it  has  sometimes  been  suggested  that  Wohler 
received  something  less  than  his  fair  share  of  credit 
for  the  work  done  with  Liebig,  the  following  extract 
from  Liebig's  autobiographic  sketch  may  fitly  close 
this  brief  account  of  their  labours  and  friendship. 

Speaking  of  his  work  at  Giessen,  he  says,  "  I  had 
the  great  good  fortune  from  the  commencement  of  my 
work  at  Giessen  to  gain  a  friend  of  similar  tastes  and 
similar  aims,  with  whom,  after  so  many  years,  I  am 
still  knit  in  the  bonds  of  warmest  affection. 

"While  in  me  the  predominating  inclination  was 
to  seek  out  the  points  of  resemblance  in  the  behaviour 
of  bodies  or  their  compounds,  he  possessed  an  unparal- 
leled faculty  of  perceiving  their  differences.  Acuteness 
of  observation  was  combined  in  him  with  an  artistic 
dexterity,  and  an  ingeniousness  in  discovering  new 


HIS    LIFE    AND   WORK.  39 

means  and  methods  of  research  or  analysis,  such  as 
few  men  possess. 

"The  achievement  of  our  joint  work  upon  uric  acid 
and  oil  of  bitter  almonds  has  frequently  been  praised  ; 
it  was  his  work.  I  cannot  sufficiently  highly  estimate 
the  advantage  which  the  association  with  Wohler 
brought  to  me  in  the  attainment  of  my  own  as  well 
as  of  our  mutual  aims,  for  by  that  association  were 
united  the  peculiarities  of  two  schools — the  good  that 
was  in  each  became  effective  by  co-operation.  Without 
envy  and  without  jealousy,  hand-in-hand,  we  plodded 
our  way  ;  when  the  one  needed  help,  the  other  was 
ready.  Some  idea  of  this  relationship  will  be  obtained 
if  I  mention  that  many  of  our  smaller  pieces  of  work 
which  bear  our  joint  names  were  done  by  one  alone ; 
they  were  charming  little  gifts  which  one  presented 
to  the  other." 

Wohler,  on  the  other  hand,  wrote  as  follows :  "  We 
two,  Liebig  and  I,  have  dissimilar  kinds  of  talent ; 
each,  when  in  concert,  strengthens  the  other.  No  one 
recognises  this  more  fully  than  Liebig  himself,  and  no 
one  does  me  greater  justice  for  my  share  of  our 
common  work  than  he." 

Assuredly  neither  of  these  two  undervalued  the 
services  rendered  to  him  by  the  other.  Their  friend- 
ship was  as  nobly  unselfish  as  it  was  useful. 


40  JUSTUS   VON   LIEBIG  : 


CHAPTER     III. 

CHEMICAL    DISCOVERIES. 

Practical  Importance  of  some  of  his  Discoveries— Method  of  Making 
Cyanide  of  Potassium— Chloroform  and  Chloral— Experiments 
on  Ammonium  Thiocyanate— Conflict  with  Gerhardt— How 
Liebig  Missed  Discovering  Bromine — Nature  of  Acids — Theory 
of  the  Polybasic  Acids — Hydrogen  Theory  of  Acids— Distinction 
of  Equivalent  from  Molecular  Weights — Progress  of  Radicle 
Theory— Ethyl  Theory — Compound  Radicles. 

IN  chemistry,  as  in  the  arts  and  manufactures,  there 
are  certain  substances  which  form,  as  it  were,  the 
raw  material  from  which  others  are  fabricated.  Thus 
salt  is  the  raw  material  for  makers  of  soda  and  soap. 
Sometimes  the  starting-point,  so  to  speak,  of  a  group 
of  manufactures  is  not  a  natural  product  like  salt,  but 
one  that  must  itself  be  prepared  on  the  large  scale 
from  other  substances.  This  is  the  case  with  yellow 
prussiate  of  potash. 

The  manufacture  of  yellow  prussiate  of  potash  on 
the  large  scale  had  long  been  practised,  but  the  nature 
of  the  changes  by  which  it  is  formed  was  first  made 
clear  by  the  experiments  of  Liebig,  with  the  result  that 
his  discovery  led  to  improvements  in  the  process, 
which  cheapened  it  and  greatly  extended  its  uses. 
One  of  its  most  important  applications  is  in  the 
making  of  potassium  cyanide.  Liebig  devised  an 
easy,  safe,  and  inexpensive  process  for  preparing  the 
latter  salt  by  melting  a  mixture  of  the  yellow  prussiate 
of  potash  with  carbonate  of  potash.  The  salt  was  thus 


HIS    LIFE    AND    WORK.  41 

made  available  for  many  new  purposes.  The  folio  whig 
are  some  striking  examples  : — 

Potassium  cyanide  dissolves  several  silver  salts 
which  are  insoluble  in  water  alone.  This  property 
was  very  useful  in  the  early  days  of  photography  ; 
photographers  made  use  of  it  for  removing  the 
unaltered  silver  compounds  from  their  negatives. 
Cheap  C}ranide  of  potassium  thus  helped  on  the  de- 
velopment of  this  useful  and  interesting  art. 

Again,  it  is  found  by  electro-platers  that  silver 
can  best  be  deposited  from  a  solution  of  silver  cyanide 
in  potassium  cyanide.  Hence  a  cheap  method  of 
making  the  cyanide  went  far  to  render  electroplating, 
practically  speaking,  possible ;  and  finally  the  low 
price  at  which  it  can  now  be  produced  enables  miners 
to  use  a  solution  of  it  for  extracting  finely  divided 
gold  from  the  rocks,  even  when  the  gold  occurs,  as  it 
often  does,  only  to  the  extent  of  less  than  one  ounce 
to  the  ton.  Thus,  without  counting  the  importance 
of  this  substance  in  pure  chemistry,  the  progress  of 
three  highly  important  branches  of  industry  have  been 
immensely  promoted  by  this  one  simple  discovery. 

Xor  does  this  example  of  the  practical  value  of 
investigations  which  at  first  sight  may  seem  to  be 
of  purely  chemical  interest  by  any  means  stand 
alone.  One  more  instance  of  even  greater  import- 
ance must  be  mentioned. 

In  1832  Liebig's  experiments  on  the  action  of 
chlorine  with  alcohol  resulted  in  the  discovery  of  a 
substance  of  absolutely  immeasurable  value  to  man — 
viz.  of  chloroform,  the  anaesthetic — and  of  a  second 
substance,  chloral,  also  of  great,  though  not  of  such 
supreme,  importance  as  the  former.  Liebig  de- 
scribed how  to  prepare  these  compounds,  and  gave 


42  JUSTUS  VON   LIEBIG: 

their  properties,*  and  he  observed  the  remarkable 
fact  that  chloral  when  it  acts  with  potash  yields 
chloroform.  Fifteen  years  afterwards,  as  we  all  know, 
chloroform  was  first  employed  as  an  ansesthetic  by 
Simpson,  of  Edinburgh.  But  it  was  not  till  twenty 
years  later  that  Oscar  Liebreich,  inspired  by  Liebig's 
observation  that  chloral  yields  chloroform  under  the 
influence  of  alkalies,  formed  the  happy  idea  of  study- 
ing its  physiological  action,  with  the  hope  that 
the  small  amount  of  alkali  in  the  blood  would  be 
sufficient  to  effect  the  transformation  of  chloral  into 
chloroform  (and  formic  acid),  with  the  result  that 
he  discovered  the  interesting  and  unexpected  physio- 
logical qualities  of  that  substance. 

It  would  be  impossible  within  the  space  which 
this  part  of  Liebig's  work  can  claim  in  this  book  to 
give  even  a  superficial  account  of  the  numerous 
substances  discovered  by  him  and  described  in  the 
three  hundred  and  eighteen  papers  that  bear  his 
name  ;  but  those  who  have  even  an  elementary  know- 
ledge of  chemistry  will  recognise  their  importance  when, 
to  mention  only  a  few,  I  say  that  they  include  such 
bodies  as  ferrocyanic  acid,  aldehyde,  meta-aldehyde, 
thialdine,  carbothialdine,  and  creatinine  and  sarcosine, 
the  decomposition  products  of  creatine  from  flesh. 

Neither  is  it  possible  to  do  justice  to  the  almost 
endless  variety  of  his  miscellaneous  observations,  to 
the  long  list  of  organic  substances  the  composition 
of  which  either  he  or  his  pupils  determined,  to  the 
numerous  plant-ash  analyses  that  were  made  in  his 
laboratory,  to  the  processes  with  which  he  endowed 
physiology,  to  his  analyses  of  German  mineral  waters, 

*  Dumas    first  correctly    determined    the   composition  of    these 
substances. 


HIS    LIFE    AND    WORK.  43 

or  to  his  contributions  to  technology,  such  as  his 
processes  for  silvering  mirrors,  and  for  making  unfer- 
mented  bread.  These  by  themselves  might  have 
made  a  reputation  for  a  not  undistinguished  man  of 
science. 

There  are, however, other  contributions  to  chemistry 
by  Liebig  of  equal  rank  with  those  which  have  been 
already  discussed.  For  example,  his  investigation 
of  the  compounds  derived  from  ammonium  sulpho- 
cyanate,  and  the  conflicts  with  Gerhard t  and  Laurent 
to  which  it  gave  rise.  And,  again,  the  part  he  played 
in  the  discussions  of  the  great  theoretical  questions 
which  followed  the  establishment  of  the  Atomic  Theory 
and  agitated  chemists  during  the  period  of  his  greatest 
activity  as  a  student  of  pure  chemistry. 

The  first  of  these  is  all  the  more  interesting  because 
it  affords  at  once  an  excellent  illustration  of  Liebig's 
method  of  work,  and  also  an  example  of  the  advan- 
tages that  often  flow  from  those  conflicts  between 
experimentally  determined  facts  on  the  one  hand,  and 
theoretical  interpretations  on  the  other ;  or  between 
old  established  views  and  new  conceptions,  which  so 
often  agitate  the  followers  of  an  active  branch  of  experi- 
mental science,  and  whose  significance  is  usually  so 
little  understood,  or  rather  so  completely  misunder- 
stood, by  the  world  at  large,  and  by  the  cynics  in 
particular. 

It  is  true  enough  that  such  struggles  are  some- 
times conducted  in  too  vehement  a  manner,  but  this 
is  not  always  nor,  indeed,  very  often  the  case. 
Besides,  is  there  not,  after  all,  a  great  element 
of  nobility  in  every  one  of  these  struggles,  in 
which  both  sides  aim  equally  at  truth,  and  both  are 
equally  free,  in  spite  of  occasional  excess  of  zeal,  from 


44  JUSTUS   VON   LIEBIG: 

all  petty  and  sordid  desires  for  personal  advantage  ? 
The  struggle  in  these  contests  is  not  to  decide  who 
shall  gain  most  advantage  from  the  result,  but  who 
shall  do  most  in  the  service  of  humanity. 

When  examining  the  effect  of  heat  and  certain 
reagents  on  ammonium  thiocyanate,  Liebig  found 
that,  instead  of  breaking  up  into  simpler  substances, 
as  he  expected,  it  gave  rise  to  a  series  of  new 
products  of  ever- increasing  complexity.  His  experi- 
ments led  him  to  give  the  following  formuke  to  the 
new  products : — 

1.  Melamine       .  .  .  C:5  N,  (NH0)3 

2.  Ammelinc       .  .  .  C8  N3  (Nil,).,  (OH) 

3.  Ammelide       .  .  .  (Co,  N3),  (NH~9)3  (OH)3 

4.  Cyanuric  Acid  .  .  C3  N3  (OH)3 

Gerhard t,  looking  at  the  formulae  given  in  the 
above  table  from  a  purely  theoretical  point  of  view, 
quickly  perceived  a  certain  want  of  symmetry  in  the 
relations  of  the  compounds  represented,  and  pointed 
out  that  the  substance  which  might  have  been  ex- 
pected to  occupy  the  third  place  in  the  table  was 
a  substance  with  the  formula  (C3N3)  (NH.,)  (OH)a, 
melanurenic  acid,  in  which  case  the  series  would  be 
written  as  follows : — 

Melamine         .  .  .  .  C3  N3  (NH2)3 

Ammoline        .  .  .  ,  QJ  N3  (NIL,)'.,  (OH) 

Melanurenic  Acid  .  .  .  C.}  N3  (NH.,)  (OH)., 

Cyanuric  Acid  .  .  .  C3  N3  (OH)3 

And  he  did  not  hesitate,  supported  only  by  theory, 
to  declare  that  Liebig's  analyses  must  be  wrong. 
Liebig  at  once  entered  a  solemn  protest  against  this 
use  of  theory  unsupported  by  experiment,  declared 
it  to  be  in  opposition  to  all  sound  principles  of 
scientific  inquiry,  and  smashed  the  critical  part  of 


HIS   LIFE   AND    WORK.  45 

the  case  of  his  antagonist  by  producing  from  urea, 
jointly  with  Wohler,  the  compound  which  Gerhard t 
had  only  imagined  to  exist,  and  showing  that  its 
properties  were  different  from  those  of  ammelide. 

But  whilst  Liebig's  reproaches  to  Gerhardt  were 
doubtless  justified,  as  regards  his  method  of  criticism, 
the  importance  of  attacking  such  subjects  from  the 
theoretical  side  is  well  shown  by  the  subsequent 
production  of  Gerhardt's  hypothetical  melanurenic 
acid.  Gerhardt's  fault  lay,  not  in  his  theorising,  but 
in  not  subjecting  his  hypothesis  to  the  test  of  rigorous 
experiment  before  attempting  to  discredit  the  experi- 
mental results  obtained  by  another. 

On  the  occasion  of  another  discussion  Liebig  again 
drew  attention  to  the  importance  of  never  trusting  an 
untested  hypothesis,  by  telling  a  story  against  himself. 
Early  in  his  career,  speculating  without  experimenting 
cost  him  and  Germany  the  discovery  of  bromine. 

"  No  greater  misfortune,"  he  said,  "  can  befall  a 
chemist  than  being  unable  to  disengage  himself  from 
preconceived  ideas,  and  yielding  to  the  bias  of  his 
mind  to  account  for  all  phenomena  not  agreeing  with 
his  conceptions  by  explanations  not  founded  on 
experiment.  .  .  I  know  a  chemist  who,  while 
at  Kreuznach  many  years  ago,  undertook  an  investi- 
gation of  the  mother-liquor  from  the  salt  works.  He 
found  iodine  in  it ;  he  observed,  moreover,  that  the 
iodide  of  starch  turned  of  a  fiery  yellow  by  standing 
overnight.  The  phenomenon  struck  him  ;  he  procured 
a  large  quantity  of  the  mother-liquor,  saturated  it 
with  chlorine,  and  obtained  by  distillation  a  consider- 
able amount  of  a  liquid  colouring  starch  yellow,  and 
possessing  the  external  properties  of  chloride  of  iodine, 
but  differing  in  many  of  its  reactions  from  the  latter 


46  JUSTUS   VON   LIEBIG: 

compound.  He  explained,  however,  every  discrepancy 
most  satisfactorily  to  himself ;  he  contrived  for  himself 
a  theory  on  it. 

"Several  months  later  he  received  the  splendid 
paper  of  M.  Balard,  and,  on  the  very  same  day,  he 
was  in  a  condition  to  publish  a  series  of  experiments 
on  the  behaviour  of  bromine  with  iron,  platinum  and 
carbon  ;  for  Balard's  bromine  stood  in  his  laboratory, 
labelled  liquid  chloride  of  iodine." 

One  of  Liebig's  most  important  contributions  to 
chemical  theory  has  already  been  brought  forward  in 
connection  with  his  joint  research  with  Wohler  upon 
oil  of  bitter  almonds.  This  has  justly  been  termed 
one  of  the  pillars  of  the  theory  of  compound  radicles. 
It  was  largely  owing  to  Liebig's  influence,  also,  that  the 
new  ideas  regarding  the  nature  of  acids  first  brought 
forward  by  our  countryman,  Sir  Humphry  Davy,  in 
1809,  were,  after  a  period  of  neglect,  once  more  pro- 
minently brought  under  the  notice  of  chemists. 

According  to  the  ideas  of  the  earlier  chemists,  all 
acids  and  all  salts  must  contain  oxygen. 

The  first  blow  at  this  conception  concerning  acids 
and  salts  was  struck  when  Davy,  after  his  famous 
investigation  of  hydrochloric  acid  and  chlorine,  re- 
nounced the  hypothetical  "  murium"  whose  oxide 
was  supposed  to  exist  in  hydrochloric  acid,  and 
boldly  represented  this  acid  as  a  combination  of  the 
element  chlorine  with  hydrogen. 

Having  observed  that  oxide  of  iodine  only  becomes 
an  acid  after  it  is  dissolved  in  water,  Davy  and  Dulong 
subsequently  went  further,  and  concluded  that  hy- 
drogen, and  not  oxygen,  is  the  true  acidifying 
element;  that  hydrogen,  in  fact,  is  the  essential 
constituent  of  acids. 


HIS   LIFE   AND  WORK.  47 

The  opinions  of  Davy  and  Dulong  on  this  subject 
were  opposed  by  Berzelius,  as  they  appeared  not  to  be 
reconcilable  with  the  electro-chemical  theory  in  which 
he  had  combined  and  developed  the  dualistic  hypo- 
thesis of  Lavoisier  and  the  electro-chemical  conception 
of  our  great  countryman  Davy,  and,  consequently, 
the  views  of  Davy  and  Dulong  lost  ground,  until 
Daniell's  studies  in  electrolysis  led  to  new  ideas  of  the 
electro-chemical  constitution  of  acids  and  salts. 

The  final  return  to  the  views  of  Davy  and  Dulong 
was  greatly  helped  on  by  the  papers  in  which  Liebig 
brought  forward  his  theory  of  the  poly  basic  acids. 

In  the  earlier  years  of  the  nineteenth  century 
most  chemists  held  views  on  the  relations  of  acids 
and  alkalies  which  practically  involved  the  assumption 
that  the  molecules  of  all  acids  are  of  equal  value  in 
their  power  of  neutralising  alkalies,  until  Graham,  in 
1833,  published  his  investigations  of  the  phosphoric 
acids,  and  showed  that  when  phosphoric  oxide  dis- 
solves in  water  it  can  generate  three  distinct  acids, 
with  very  different  powers  of  neutralising  alkalies. 

Liebig,  in  1837,  paid  a  visit  to  England,  when  he 
formed  a  high  opinion  of  Graham,  of  whom  he  says, 
"  Graham  .  .  .  modest  and  without  pretence, 
makes  wonderful  discoveries."  About  the  same  time 
he  visited  Paris  and  Dumas,  and  from  a  letter  written 
to  Wohler,  after  his  return,  it  would  appear  that  he 
then  began  to  form  new  views  on  the  constitution  of 
the  acids.  In  the  same  year  he  published,  jointly 
with  Dumas,  a  paper  in  which  they  proposed  that 
the  accepted  formula  for  citric  acid  should  be  trebled, 
thus  making  this  a  tribasic  acid.*  Liebig  afterwards 

*  Note. — The  neutralising  power  of  a  molecule  of  a  dibasic  acid 
is  twice  as  great  as  that  of  a  molecule  of  a  monobasic  acid,  and  so  on. 


48  JUSTUS   VON   LIEBIG: 

returned  to  the  subject,  and  described  experiments 
with  a  whole  host  of  acids  and  their  salts,  in  which 
the  existence  of  monobasic,  dibasic,  and  tribasic 
organic  acids  was  clearly  indicated,  and  in  the 
course  of  his  work  he  soon  saw  that  the  hydrogen 
theory  of  acids  was  both  probable  and  convenient. 
Acids  he  denned  as  particular  compounds  of 
hydrogen,  in  which  the  latter  can  be  replaced  by 
metals. 

It  was  at  one  time  objected  that  Davy's  theory 
involved  the  necessity  of  admitting  the  existence 
of  a  host  of  radicles  which  had  not  been,  and  in 
most  cases  still  have  not  been,  isolated ;  but  this, 
as  Liebig  pointed  out,  was  equally  true  of  the 
earlier  view.  Very  few  of  the  acid  anhydrides  Aviiich 
were  supposed  to  enter  into  the  formation  of  salts 
had  at  that  time  been  discovered,  whilst  in  addition 
the  experimental  evidence  which  could  then  be 
brought  forward  was  all  against  the  existence  of  such 
hypothetical  elements  as  the  "  murium,"  which  was 
supposed  to  be  a  constituent  of  the  hypothetical  acid 
anhydride  of  the  chlorides.  To  support  the  earlier, 
and  at  that  time  more  orthodox,  view  it  was  necessary 
not  only  to  admit  the  existence  of  non-isolated 
radicles,  but  also  to  invent  non-existent  elements 
from  which  to  construct  them.  Hypothesis  had  to 
be  supported  by  hypothesis.  It  was  natural,  there- 
fore, that  Liebig,  who  was  ever  forward  in  denouncing 
such  a  use  of  theory  in  science,  should  be  amongst 
the  foremost  of  those  who  supported  the  new  con- 
ceptions which  were  more  securely  based  on  the 
proved  truths  of  chemical  science. 

The  chemists  of  to-day — nay,  even  comparatively 
young  students  of  the  subject — are  accustomed  to 


HIS    LIFE    AND    WORK.  49 

distinguish  with  precision  between  the  chemical 
conceptions  of  the  molecule,  the  atom,  and  the 
equivalent.  When  Graham  and  Liebig  worked  on 
phosphoric  and  the  organic  acids,  far  less  distinct 
notions  prevailed  on  the  subject,  and  especially  on 
the  proper  employment  of  the  terms  "equivalent" 
and  "atom." 

The  term  atom  was,  as  has  previously  been  ex- 
plained, introduced  into  chemistry  by  John  Dalton 
to  designate  certain  very  small  indivisible  particles 
of  which  matter  is  supposed  to  be  composed.  Dalton 
considered  that  chemical  compounds  were  formed  by 
the  uniting  or  approximating  of  atoms  of  different 
elements,  and  that  the  atoms  of  each  element  were 
exactly  alike  in  all  their  properties,  including  their 
weight.  He  published  certain  tables  in  which  he 
professed  to  give  the  relative  weights  of  the  atoms. 
These  numbers  were  calculated  from  the  relative  pro- 
portions of  the  elements  found  in  their  compounds. 
Wollaston,  in  1808,  and  afterwards  Davy  and  Gay- 
Lussac,  denied  that  Dalton's  atomic  weights  were 
really  the  relative  weights  of  the  atoms,  and  Wollaston 
proposed  for  them  the  name  chemical  equivalents. 
The  use  of  this  term  was  not,  however,  always  con- 
fined to  its  original  purpose ;  it  came  to  be  extended 
to  compound  substances  as  well  as  to  the  elements. 
Thus  it  happened  that  when  the  word  was  applied  to 
elements,  it  was  apt  to  be  used  very  much  in  the 
early  sense  of  the  term  atomic  weight;  whilst  as 
applied  to  compounds,  it  often  signified  more  nearly 
what  we  now  define  as  the  molecular  weight.  The 
clearing  -  up  of  the  confusion  thus  created  was 
initiated  by  Liebig,  to  whom  we  owe  the  first 
precise  expressions  of  the  distinction  between  the 


50  JUSTUS   VON   LIEBIG: 

equivalent  weights   and   the   molecular   weights*  of 
substances. 

One  of  the  most  interesting  discussions  in  which 
Liebig  assisted  related  to  the  constitution  and  relations 
of  alcohol  and  ether. 

L  According  to  Liebig,  the  relation  of  these  organic 
compounds  to  the  inorganic  substances  is  very  simple 
and  intelligible.  They  contain  a  compound  radicle, 
ethyl  (CoIL^  alcohol  being  its  hydroxide  and  ether 
xide.  ±L.thyl  may  be  compared  to  the  element 
potassium,  and  its  compounds  to  those  of  potassium. 
Thus— 

Ether  (C2H5)20          corresponds  to  the  oxide  K2O. 
Alcohol  (C2H5) OH  ,,  „        hydroxide  KHO. 

Ethyl  chloride  (C2H5)C1     „  „         chloride  KC1. 

He  did  not,  it  is  true,  at  once  arrive  at  the 
"ethyl  theory"  exactly  as  stated  above.  Still,  the 
modern  view  is  in  all  its  essentials  founded  solely 
on  the  views  of  Liebig,  according  to  which  organic 
chemistry  was  defined  as  the  "chemistry  of  organic 
radicles,"  whilst  these  radicles  were  compared 
with  the  elements,  and  their  combinations  with 
the  corresponding  inorganic  substances.  "  Organic 
chemistry,"  said  Liebig  and  Dumas,  "  possesses  its  own 
elements,  which  sometimes  play  the  part  of  chlorine 
or  oxygen,  sometimes  that  of  a  metal.  Cyanogen, 
amidogen,  benzoyl,  and  the  radicles  of  ammonium  com- 
pounds, of  fats,  and  of  alcohol  and  its  derivatives,  con- 
stitute the  true  elements  of  organic  nature " 

*  Liebig  used  the  word  atom  in  his  writings  where  we  use  mole- 
cule, for  the  exact  distinction  between  atoms  and  molecules  was 
accomplished  later  by  his  successors. 


HIS   LIFE    AND    WORK.  51 


CHAPTER  IV. 

L1EBIG    AND    DUMAS. 

Dumas's  Early  Life — Dumas  at  Geneva — His  Meeting  with  Hum- 
boldt — Paris  —  Substitution  —  Conflict  with  Dualism  — Li  ebig 
accepts  Substitution  Theory — Chemistry  of  Vinegar-making 
— Aldehyde. 

THE  two  chemists  who  were  chiefly  associated  with 
Liebig  in  directing  the  course  of  organic  chemistry 
during  the  third  and  fourth  decades  of  the  nineteenth 
century  were  Wohler,  in  Germany,  and  Dumas,  in 
France.  Wohler  and  Liebig  almost  from  the  time 
of  their  first  meeting  were,  as  we  have  seen,  closely 
knit  in  friendship,  and  for  many  years  were  intimately 
associated  in  the  prosecution  of  common  studies. 

The  relations  of  Liebig  and  Dumas  were  not 
always  equally  harmonious  ;  these  two  sometimes 
found  themselves  in  opposite  camps.  Both  of  them 
were  men  who  could  take  as  well  as  give  hard 
knocks,  however,  and  hence  their  frequent  scientific 
encounters  never  prevented  either  of  them  from  appre- 
ciating the  high  qualities  of  the  other,  and  on  several 
occasions  they  worked  in  unison  for  a  common 
object.  When  Liebig  dedicated  a  German  edition  of 
his  "  Familiar  Letters  on  Chemistry  "  to  Dumas,  in 
1851,  Avith  characteristic  open-heartedness  he  ad- 
dressed the  following  note  to  his  old  opponent : — 

"  MY  DEAR  DUMAS,— It  was  by  a  strange  coincidence  that 
for  more  than  a  quarter  of  a  century  our  labours  in  the  cause 


52  JUSTUS  VON  LIEBIG: 

of  the  science  to  which  our  lives  have  been  devoted  were 
prosecuted  in  the  same  direction. 

"  If  the  roads  by  which  we  endeavoured  to  attain  the  goal 
were  often  different,  in  the  proximity  of  that  goal  we  always  met 
in  order  to  shake  hands  with  each  other. 

"  Not  only  your  country,  but  the  whole  scientific  world, 
acknowledges  the  range,  the  depth,  and  the  importance  of  your 
researches  and  discoveries,  but  no  one  knows  better  than  myself 
the  obstacles  which  your  genius  had  to  surmount  in  order  to 
achieve  those  inestimable  conquests  which,  in  a  measure,  con- 
stitute the  foundation  of  modern  science.  Though  contending 
with  difficulties  of  every  kind,  )ou  never  descended  into  the 
arena  without  leaving  it  as  conqueror. 

"  Permit  me,  in  recognition  of  the  services  which  you  have 
rendered  to  science  and  to  mankind  at  large,  to  dedicate  to  you 
this  little  work,  in  which  I  have  ventured  to  sketch  for  an 
enlarged  circle  of  readers  the  onward  movement  of  scientific 
and  applied  chemistry,  to  which  you  have  so  much  contributed. 
Your  approbation  would  be  the  highest  reward  I  could  possibly 
hope  for.  "  LIEBIG. 

"  Giessen,  1851." 

Whilst  Durnas.  not  less  generous  than  his  old 
friend  and  opponent,  when  referring  to  their  labours 
in  organic  chemistry  in  his  commemorative  speech  on 
Pelouze,  said : — 

"  Into  this  as  yet  uncultivated  domain  we  had 
plunged,  Liebig  and  I,  with  most  living  ardour.  The 
number  of  organic  substances,  nowadays  immense,  was 
even  then  very  considerable.  Their  study,  however, 
if  we  except  the  group  of  bodies  selected  by  Chevreul 
for  his  researches, had  not  as  yet  elicited  results  of  any 
great  importance.  The  nature  of  most  compounds 
was  unknown ;  their  differences,  their  analogies, 
their  connections  had  still  to  be  unveiled." 

"  To  find  our  way  through  these  unexplored  terri- 
tories, we  had  neither  compass  nor  guides,  neither 
method  nor  laws.  Each  of  us  had  been  led  to  form 


HIS    LIFE   AND   WORK.  53 

ideas  and  to  elaborate  views  peculiar  to  himself,  which 
he  defended  with  warmth  and  even  with  passion  but 
without  any  feeling  of  envy  or  jealousy.  The  dis- 
coveries to  be  made  appeared  to  us  without  limit, 
and  each  was  satisfied  with  his  harvest.  What  we 
both  had  at  heart  was  to  stake  the  ground  and  open 
roads,  nor  have  I  any  doubt  that  in  reading  my 
papers  Liebig  felt  the  same  pleasure  which  the 
perusal  of  his  afforded  me.  If  a  new  step  had  been 
taken,  it  was  of  little  moment  whether  it  had  been 
made  by  the  one  or  by  the  other,  since  it  served  us 
both  on  the  road  to  truth." 

Jean  Baptiste  Andre  Dumas  was  born  at  Alais,  in 
the  department  of  the  Gard,  July  14th,  1800,  and,  like 
Liebig.  became  apprentice  to  an  apothecary ;  but  not 
finding  much  opportunity  for  scientific  progress  in  his 
position  he  soon  migrated  to  Geneva,  travelling  there 
on  foot.  Here  he  found  both  employment  and  means 
of  education,  and  very  quickly  developed  in  a  surpris- 
ing degree  his  talent  for  experimental  investigation. 

The  turning-point  in  the  career  of  Liebig  was,  as 
we  have  seen,  probably  his  meeting  with  Alexander 
von  Hurnboldt  and  his  introduction  by  the  latter  to 
Gay-Lussac  in  1823.  Singularly  enough,  it  was  a  day 
spent  with  the  great  traveller  which  induced  Dumas 
to  turn  his  face  to  Paris  at  a  moment  when  there  was 
much  to  induce  him  to  settle  in  Geneva. 

The  story  of  their  meeting  was  told  by  Dumas 
himself  to  Hofmann,  and  it  illustrates  so  well  the 
fascination  that  Humboldt  could  exercise  on  a  youth 
of  genius  that,  though  it  is  rather  foreign  to  the 
purpose  of  this  book,  it  must  not  be  omitted  :— 

"  One  day,"  said  Dumas, "  when  I  was  in  my  study 
completing  some  drawings  at  the  microscope,  and,  it 


54  JUSTUS   VON   LIEBIG  : 

must  be  added,  rather  negligently  attired  to  enable 
me  to  move  more  freely,  some  one  mounted  the 
stairs,  stopped  on  my  landing,  and  .gently  knocked  at 
the  door.  '  Come  in/  said  I,  without  looking  up  from 
my  work.  On  turning  round  I  was  surprised  to  find 
myself  face  to  face  with  a  gentleman  in  a  bright 
blue  coat  with  metal  buttons,  a  white  waistcoat, 
nankeen  breeches,  and  top  boots.  This  costume, 
which  might  have  been  the  fashion  under  the  Direc- 
tory, was  then  quite  out  of  date.  The  wearer  of  it,  his 
head  somewhat  bent,  his  eyes  deep  set  but  keen, 
advanced  with  a  pleasant  smile,  saying,  '  Monsieur 
Dumas  ? '  '  The  same,  sir  ;  but  excuse  me/  '  Don't 
disturb  yourself.  I  am  M.  de  Humboldt,  and  did  not 
wish  to  pass  through  Geneva  without  having  had  the 
pleasure  of  seeing  you.'  Throwing  on  my  coat,  I 
hastily  reiterated  my  apologies.  I  had  only  one  chair ; 
my  visitor  was  pleased  to  accept  it,  whilst  I  resumed 
my  elevated  perch  on  the  drawing  stool.  Baron 
Humboldt  had  read  the  paper  published  by  M.  Prevost 
and  myself,  on  blood,  and  was  anxious  to  see  the 
preparations  I  had  by  me.  His  wish  was  soon  grati- 
fied. '  I  ara  going  to  the  Congress  at  Verona/  said  he, 
1  and  I  intend  to  spend  some  days  at  Geneva,  to  see 
old  friends  and  make  new  ones,  and  more  especially 
to  become  acquainted  with  young  people  who  are 
beginning  their  career.  Will  you  act  as  my  cicerone  ? 
I  warn  you,  however,  that  my  rambles  begin  early 
and  end  late.  Now,  could  you  be  at  my  disposal, 
say,  from  six  in  the  morning  till  midnight  ? '  This 
proposal,  which  was,  of  course,  accepted  with  alacrity, 
proved  to  me  a  source  of  unexpected  pleasure.  Baron 
Humboldt  was  fond  of  talking;  he  passed  from  one 
subject  to  another  without  stopping.  He  obviously 


HIS    LIFE    AND   WORK.  55 

liked  being  listened  to,  and  there  was  no  fear  of  his 
being  interrupted  by  a  young  man  who,  for  the  first 
time,  heard  Laplace,  Berthollet,  Gay-Lussac,  Arago, 
Thenard,  Cuvier,  and  many  others  of  the  Parisian 
celebrities,  spoken  of  with  familiarity.  I  listened  with 
a  strange  delight ;  new  horizons  began  to  dawn  upon 
me.  .  ." 

"  At  the  end  of  a  few  days  Baron  Humboldt  left 
Geneva.  After  his  departure  the  town  seemed  empty 
to  me.  I  felt  as  if  spellbound.  .  .  I  had  been  more 
especially  impressed  with  what  he  told  me  of  Parisian 
life,  of  the  happy  collaboration  of  men  of  science,  and 
of  the  unlimited  facilities  which  the  French  capital 
offered  to  young  men  wishing  to  devote  themselves  to 
scientific  pursuits.  I  began  to  think  that  Paris  was 
the  only  place  where,  under  the  auspices  of  the  leaders 
of  physical  and  chemical  science,  with  whom,  I  had  no 
doubt,  I  should  soon  become  acquainted,  I  might 
hope  to  find  the  advice  and  assistance  which  would 
enable  me  to  carry  out  the  labours  over  which  I  had 
been  pondering  for  some  time.  My  mind  was  made 
up  :  I  must  go  to  Paris." 

In  the  year  1823,  therefore,  Dumas  went  to  Paris. 
Before  long  he  obtained  the  appointment  of  Repetiteur 
de  Chimie  to  Thenard's  course  of  Lectures  in  the  ficole 
Polytechnique.  From  this  time  his  attention  was 
directed  to  the  study  of  chemical  phenomena. 

Such  were  the  first  steps  of  Liebig's  great  colleague 
and  rival,  Dumas. 

If  Liebig  had  so  frequently  the  happiness  of  wit- 
nessing the  triumph  of  his  ideas,  and  had  so  often  the 
gratification  of  observing  the  development  of  organic 
chemistry  proceed  along  the  lines  which  he  himself 
had  laid  down,  on  the  other  hand,  he  occasionally 


56  JUSTUS  VON   LIEBIG: 

found  it  necessary  at  the  end  of  a  discussion  to 
accept  the  conclusions  of  others  or  to  remain  opposed 
to  the  truth.  At  such  times  he  never  hesitated; 
once  let  him  be  convinced  of  the  justness  of  the  views 
of  an  opponent,  and  he  was  among  the  very  foremost 
to  welcome  an  advance,  or  the  discovery  of  a  new 
road,  into  the  unknown.  This  quality  of  his  mind 
is  well  illustrated  by  his  attitude  to  the  theory  of 
substitution,  which  in  the  hands  of  Dumas  and  his 
successors  effected  the  final  overthrow  of  the  dualistic 
view  of  chemical  phenomena,  and  greatly  modified 
the  early  form  of  the  theory  of  compound  radicles 
itself. 

The  dualistic  idea  was  introduced  into  chemistry 
by  Lavoisier ;  it  reached  its  highest  development  in 
the  hands  of  Wohler's  master,  Berzelius.  According 
to  Lavoisier,  however  great  may  be  the  complexity  of 
a  compound  we  may  always  detect  in  it  evidence  of 
two  constituent  parts.  These  may  be  either  simple, 
as  in  the  oxides — e.g.  oxide  of  calcium,  or  quicklime, 
which  contains  a  non-metal,  oxygen,  united  with  a 
metal,  calcium — or  compound,  as  in  the  salts,  which 
he  regarded  as  produced  by  the  union  of  an  oxide  of 
a  metal,  on  the  one  hand,  with  an  acid  (usually  the 
oxide  of  a  non-inetal)  on  the  other.  Early  in  the 
century  Berzelius,  by  his  electro-chemical  theory, 
had  offered  an  explanation  of  dualistic  combina- 
tion which  was  consistent  with  the  knowledge  of 
electrolysis  then  possessed  by  chemists,  and  thus  re- 
established the  position  of  dualism  in  the  science  at 
a  moment  when  it  seemed  to  be  seriously  threatened 
by  the  new  facts  which  had  lately  been  brought  to 
light  by  the  investigations  of  Davy. 

Berzelius   started  with   the   assumption  that  the 


HIS    LIFE    AND   WORK.  57 

atoms  are  themselves  electric,  and  possess  at  least 
two  poles  whose  quantities  of  electricity  are  in  most 
cases  unequal.  Thus  the  elements  could  be  classed  as 
positive  and  negative  according  to  which  electricity 
prevailed.  Chemical  combination,  according  to  this 
theory,  consists  in  the  attraction  of  the  dissimilar 
poles  of  the  atoms,  and  consequently  in  the  neutral- 
ising of  the  two  electricities.  As,  however,  these 
were  not  always  equal  in  amount,  the  compound  pro- 
duced was  itself  frequently  electric,  and  therefore 
capable  of  entering  into  further  combinations.  Thus, 
according  to  Berzelius,  each  compound  consists  of  two 
different  parts,  as  suggested  by  Lavoisier,  which  attract 
each  other  in  consequence  of  their  different  states  of 
electrification. 

In  accordance  with  these  ideas  Berzelius  repre- 
sented the  composition  of  salts  by  such  formulae  as 
the  following,  in  which  the  electro-chemical  form  of 
the  dualistic  view  of  chemical  combination  will  at 

once  be  recognised : — 

i       

Barium  sulphate        Ba  O  S03 

+       - 
Calcium  sulphate       Ca  O  SO3 

+       — 
Copper  sulphate          Cu  O  SO3 

When  organic  chemistry  began  to  develop  in  the 
hands  of  Liebig,  Wohler,  and  the  French  chemists, 
Berzelius  directed  his  attention  especially  to  the 
task  of  bringing  the  radicle  theory  of  organic 
chemistry  into  agreement  with  the  fundamental 
ideas  of  his  electro-chenrical  form  of  dualism. 
According  to  him  compound  radicles  were  unalter- 
able groups,  and  he  thought  that  organic  chemistry, 
like  inorganic  chemistry,  must  accept  oxygen  as  the 


58  JUSTUS   VON   LIEB1G: 

supreme  ruler  among  the  elements,  and  give  it  the 
place  which  it  had  held  in  the  mineral  world  since 
the  time  of  Lavoisier. 

But,  meanwhile,  new  departures  were  imminent 
which  were  fated  to  work  great  changes  in  the  radicle 
theory  almost  before  it  had  come  to  maturity. 

One  evening,  at  a  soiree  at  the  Tuileries,  during  the 
reign  of  Charles  X.,  the  pleasure  of  the  entertain- 
ment was  seriously  marred  by  the  fact  that  the  wax- 
candles  emitted  very  unpleasant,  irritating  fumes,  and 
were  remarkable  for  the  smokiness  of  their  flames. 
The  investigation  of  the  cause  of  their  peculiar  be- 
haviour was  entrusted  to  Dumas.  The  irritating 
fumes  were  found  to  be  hydrochloric  acid,  and  Dumas 
had  no  difficulty  in  discovering  that  they  were 
due  to  the  candles  having  been  made  from 
wax  which  had  been  bleached  by  chlorine.  This 
circumstance  led  him  to  investigate  the  action  of 
chlorine  upon  organic  bodies.  He  soon  found  that, 
when  chlorine  acts  on  compounds  containing  hydro- 
gen, the  hydrogen  may  be  removed  and  replaced  by 
an  equivalent  quantity  of  chlorine.  This  observation 
was  not,  it  is  true,  a  new  one ;  Gay-Lussac,  Faraday, 
and  Liebig  and  Wohler  had  all  observed  that  hydro- 
chloric acid  is  emitted,  and  chlorine  fixed  by  organic 
bodies.  But  Dumas  first  systematically  examined 
this  kind  of  action,  laid  down  the  rules  which  it 
follows,  and,  jointly  with  Laurent,  who  first  perceived 
their  significance,  developed  their  consequences.  How 
was  it  possible,  they  asked,  to  continue  to  accept 
the  electro-chemical  hypothesis,  with  its  rigidly  ap- 
pointed and  opposite  functions  for  electro-positive  and 
electro-negative  elements,  when  it  was  thus  shown 
to  be  possible  for  an  electro-negative  atom,  like  that 


HIS    LIFE   AND   WORK.  59 

of  chlorine,  to  replace  an  electro-positive  atom  of 
hydrogen  ? 

Dumas'  earliest  results  were  soon  splendidly  con- 
firmed hy  the  discovery  of  trichloracetic  acid.  By 
suitably  treating  acetic  acid  with  chlorine  Dumas 
produced  from  it  another  acid,  which  differed  from 
the  first  by  containing  three  atoms  of  chlorine  in 
place  of  three  atoms  of  hydrogen  in  every  molecule. 
"  It  is  chlorinated  vinegar,"  said  Dumas ;  "  but 
what  is  very  remarkable,  at  least  for  those  who 
refuse  to  find  in  chlorine  a  body  capable  of  replacing 
hydrogen  in  the  precise  and  complete  sense  of  the 
word,  this  chlorinated  vinegar  is  jxist  as  much  an 
acid  as  common  vinegar  itself.  Its  acid  power  is  not 
changed.  It  saturates  the  same  quantity  of  alkali  as 
before,  and  saturates  it  equally  well,  and  the  salts  to 
which  it  gives  rise  exhibit,  when  compared  with 
acetates,  resemblances  full  of  interest  and  gener- 
ality." 

"  Here,  then,  is  a  new  organic  acid,  containing  a 
very  considerable  quantity  of  chlorine,  and  exhibiting 
none  of  the  reactions  of  chlorine ;  its  hydrogen  has 
disappeared,  and  has  been  replaced  by  chlorine,  and 
yet  this  remarkable  substitution  has  produced  only 
a  slight  change  in  its  properties,  all  its  essential 
characters  remaining  unaltered." 

"  If  its  internal  properties  are  modified,  this  modi- 
fication becomes  apparent  only  when,  through  the 
intervention  of  a  new  force,  the  molecule  itself  is 
destroyed  and  transformed  into  neAv  products  .  .  . 
It  is  evident  that,  in  confining  myself  to  this  system 
of  ideas  dictated  by  facts,  I  have  not  in  any  way 
taken  into  consideration  the  electro-chemical  theories 
on  which  Berzelius  has  generally  based  the  idea 


60  JUSTUS   VON   L1EBIG: 

predominating  in  the  opinions  which  this  illustrious 
chemist  has  endeavoured  to  enforce." 

"  But  do  these  electro-chemical  ideas,  this  special 
polarity  attributed  to  the  molecules  of  elementary 
bodies,  rest  upon  facts  so  evident  that  it  is  necessary 
to  erect  them  into  articles  of  faith  ?  Or,  if  they  must 
be  regarded  as  hypotheses,  have  they  the  power  of 
lending  themselves  to  facts,  of  explaining  and  fore- 
seeing them  with  so  complete  a  certainty  as  to  have 
afforded  important  assistance  in  chemical  researches  ? 
It  must  plainly  be  allowed  that  this  is  not  the  case." 

At  first  Berzelius  received  these  new  ideas  with 
something  like  disdain.  Such  assertions,  put  forward 
as  they  were  at  first  by  Laurent,  a  beginner,  were  still 
without  authority ;  they  appeared  to  him  unworthy 
of  serious  refutation.  But  when  Dumas  came  into 
the  field,  Berzelius  energetically  defended  his  opinions. 
In  this  he  was  at  first  vigorously  supported  by  Liebig, 
who  admitted,  indeed,  the  fact  of  substitution,  but 
protested  against  the  wide  conclusions  Dumas  drew 
from  his  results,  and  met  him  with  an  ironical  re- 
joinder in  the  form  of  a  letter,*  purporting  to  come 
from  S.  C.  H.  Windier,  which  ran  much  as  follows : — 

"  The  last  great  discovery  from  Paris  shows  that  it 
has  been  found  possible  to  replace  in  acetate  of  man- 
ganese first  the  atoms  of  hydrogen  by  chlorine,  then 
the  oxygen,  then  the  manganese,  and  at  last  even  the 
carbon,  so  that  a  body  was  formed  which  contained 
only  chlorine,  but  retained  still  the  properties  of  the 
original  substance."  He  continued,  after  alluding  to 
the  method  of  bleaching  cotton  goods  by  chlorine  :  "  I 
understand  that  there  are  already  in  the  London  shops 
stuffs  made  of  chlorine  thread  much  approved  in 

*  Tliis  letter  was  written  by  Wohler,  and  published  by  Liebig.  W 


HIS    LIFE    AND    WORK.  61 

the  hospitals  and  preferred  to  all  others  for  night- 
caps, under-garments,  etc." 

However,  further  facts,  such  as  the  re-converting 
of  chloracetic  acid  into  acetic  acid  by  the  action  of 
nascent  hydrogen,  and  especially  the  production  of  the 
chlorine  and  bromine  derivatives  of  aniline  in  his 
own  laboratory  by  his  pupil,  Hofmann,  before  long 
convinced  Liebig  that  the  character  of  a  chemical 
substance  does  not  depend  so  much  as  he  had  supposed 
on  the  nature  of  its  constituent  atoms,  but  very  largely 
also  on  the  manner  in  which  these  atoms  are  arranged, 
and  he  declared  that  the  interpretations  proposed  by 
Dumas,  of  the  facts  relating  to  substitution,  appeared 
to  him  to  afford  the  explanation  of  a  great  number  of 
phenomena  in  organic  chemistry. 

Some  years  afterwards,  at  a  dinner  given  by  the 
French  chemists  to  chemical  visitors  to  the  Exhibition 
of  1867,  Liebig  made  his  defeat  on  this  occasion  the 
source  of  a  happy  retort  to  Dumas,  who  had  asked 
him  why  of  late  years  he  had  devoted  himself  exclu- 
sively to  agricultural  chemistry.  "  I  have  withdrawn 
from  organic  chemistry,"  said  Liebig,  "for  with  the 
theory  of  substitution  as  a  foundation,  the  edifice  of 
chemical  science  may  be  built  up  by  workmen :  masters 
are  no  longer  needed" 

Of  course,  this  must  be  taken  in  the  spirit  of 
the  after-dinner  speech ;  but  the  reply  shows  the 
completeness  with  which  Liebig  extended  his  ad- 
miration to  a  great  achievement,  even  when  it  had 
not  been  reached  without  some  little  opposition  from 
himself  and  some  damage  to  his  own  ideas. 

To  conclude  this  long  list  of  some  of  Liebig's  chief 
contributions  to  pure  chemistry,  which,  as  will  pre- 
sently be  seen,  only  represents  a  part  of  the  field 


62  JUSTUS   VON   LIEBIG: 

covered  by  his  work,  we  must  now  glance  at 
his  inquiry  into  the  chemistry  of  the  change  of 
alcohol  into  vinegar.  This  subject  closes  most 
suitably  an  account  of  Liebig's  labours  in  chemistry, 
because  it  leads  us  by  a  natural  transition  to  a 
chemico-biological  inquiry  in  which  he  took  a  promi- 
nent part — viz.  to  the  question  of  the  nature  of 
fermentation. 

It  has  long  been  a  familiar  fact  that  moderately 
dilute  solutions  of  alcohol,  such  as  wine  or  beer,  when 
exposed  to  the  air,  become,  under  certain  conditions, 
converted  into  vinegar,  but  the  exact  nature  of  the 
chemical  changes  involved  for  long  remained  unex- 
plained. 

Liebig  soon  dispelled  the  obscurity  in  which  this 
subject  had  so  long  remained,  by  showing  that  the 
change  from  alcohol  to  vinegar  (acetic  acid)  takes 
place  in  two  stages,  viz.  that  when  alcohol  is 
submitted  to  the  action  of  an  oxidising  agent — to 
the  action  of  a  substance  which  readily  parts  with 
oxygen,  that  is  to  say — it  first  loses  hydrogen,  which 
is  removed  in  the  form  of  water,  by  which  change  a 
substance  called  aldehyde  is  produced ;  and,  secondly, 
that  the  aldehyde  takes  up  oxygen  to  form  acetic 
acid.  Frequently,  of  course,  these  two  changes  pro- 
ceed simultaneously,  so  that  they  become  indistin- 
guishable, but  by  suitable  methods  Liebig  secured 
the  intermediate  product,  and  by  doing  so  presented 
to  us  a  new  substance,  which  has  given  its  name  to  a 
class — the  aldehydes — and  still  remains  in  the  minds 
of  chemists  as  the  aldehyde  par  excellence.  One 
useful  quality  of  aldehyde,  which  Liebig  was  the 
first  to  observe  and  employ,  must  be  mentioned.  If 
one  adds  a  few  drops  of  aldehyde  to  a  flask  or 


HIS    LIFE    AND    WORK.  63 

test-tube  containing  a  solution  of  lunar  caustic — 
nitrate  of  silver — rendered  slightly  ammoniacal  by 
an  addition  of  ammonia,  and  then  gently  warms  the 
mixture,  at  once  the  glass  becomes  coated  with  a  film 
of  silver,  reflecting  more  perfectly  than  an  ordinary 
mercury  mirror.  This  reaction  affords  both  a  useful 
test  for  aldehyde .  and  a  ready  and  simple  method  of 
preparing  mirrors  which  is  often  useful,  and  makes  it 
possible  to  avoid  the  danger  to  health  and  life  attached 
to  the  older  process  in  which  mercury  is  used. 


64  JUSTUS   VON   LIEBIO: 


CHAPTER     V. 

FERMENTATION. 

Liebig's  Theory  of  Fermentation — Supposed  Influence  of  Oxygen — 
Difference  between  Fermentation  and  Decay — Fermentation 
of  Alcohol — "  Quick  Vinegar  Process  " — The  Vitalistic  Theory 
revived  by  Pasteur — Discussion  between  Liebig  and  Pasteur — 
Lactic  Ferment — Vinegar  Plant — Enzymes. 

FERMENTATION. — The  word  fermentation  is  derived 
from  fervere,  "  to  boil,"  and  may  be  supposed  to  owe  its 
origin  to  the  effervescence  which  occurs  when  saccharine 
liquids  are  left  to  themselves  in  contact  with  air,  or 
placed  in  contact  with  a  ferment  such  as  yeast. 
Naturally,  such  a  wonder-working  process  as  fermen- 
tation has  always  attracted  the  interest  of  the  observant, 
and  numerous  indeed  have  been  the  conjectures 
hazarded  in  the  various  attempts  which  have  been 
made  to  fathom  its  mystery.  It  was  impossible,  how- 
ever, as  will  soon  be  seen,  that  much  real  progress 
should  be  made  by  the  earlier  thinkers  on  the  subject, 
for,  only  when  the  microscope  had  been  brought  to  a 
state  of  considerable  efficiency,  and  when,  at  least,  a 
good  start  had  been  made  in  organic  chemistry,  was 
it  possible  to  get  any  light  on  this  absorbing  yet 
bewildering  subject. 

To  many  the  word  fermentation  still  implies  very 
little ;  to  most  it  probably  merely  connotes  the  useful 
process  by  which  the  sugar  of  malt  or  of  grapes  is 
converted  into  beer  or  wine,  or  by  which  flour  and 
water  are  made  to  yield  bread ;  or  again,  the  pernicious 


HIS   LIFE    AND' WORK.  65 

change  by  which  badly  made  preserves  are  apt  to  lose 
their  attractiveness  of  flavour  and  become  both  dis- 
tasteful and  unwholesome.  It  is,  therefore,  necessary 
to  explain  that  these  are  only  a  few  instances  from  a 
very  large  class  of  diverse  changes,  all  of  them  brought 
about  by  substances  or  organisms  known  to  chemists 
and  biologists  as  the  "ferments." 

According  to  Liebig,  fermentation  is  to  be  con- 
sidered an  essentially  chemical  phenomenon ;  accord- 
ing to  his  opponents,  fermentive  changes  depend,  in 
many  cases  at  least,  on  the  life-processes  of  certain 
minute  organisms.  To  the  latter,  therefore,  ferment- 
ation, in  these  cases  at  any  rate,  is  not  a  chemical,  but 
rather  a  biological,  phenomenon. 

It  is  one  of  the  distinguishing  features  of  a  "  fer- 
ment "  that  a  very  little  of  it  goes  a  long  way.  A 
minute  fragment  of  rennet  is  sufficient  to  cause  the 
curdling  of  a  relatively  large  quantity  of  milk.  A 
single  yeast  cell  may  bring  about  the  fermentation  of 
the  largest  vessel  of  grape  juice,  and  presently  the 
grape  juice  will  be  converted  into  wine.  If  but  the 
point  of  a  needle  touch  a  liquid  in  which  the  ferment 
of  anthrax  has  been  cultivated,  a  prick  from  that 
needle  will  be  sufficient  to  communicate  anthrax  to 
any  animal  susceptible  to  the  disease. 

These,  and  others  like  them,  are  the  phenomena 
which  must  be  explained  by  a  theory  of  fermen- 
tation. 

An  early  attempt  to  explain  these  fermentive 
changes  chemically  was  that  of  Berzelius.  Lavoisier 
having  shown  that  sugar  is  split  up  by  fermentation 
into  alcohol  and  carbonic  acid  gas,  Berzelius  sug- 
gested that  the  action  of  the  yeast  is  "catalytic" 
—that  is,  that  the  ferment  brings  about  the  de- 


b6  JUSTUS   VON   LIEBIG: 

composition  of  the  sugar,  by  mere  contact,  much  as 
platinum  black  causes  hydrogen  peroxide  to  decom- 
pose into  water  and  oxygen,  or  as  manganese  dioxide 
causes  chlorate  of  potassium  to  give  up  its  oxygen 
at  a  lower  temperature  than  is  required  for  the  decom- 
position of  the  salt  by  heat  alone.  For  some  time  this 
so-called  explanation  of  the  phenomenon  seems  to 
have  been  accepted  as  satisfactory,  but  inasmuch  as 
the  nature  of  a  catalytic  action  was  not  itself  under- 
stood, it  did  not  in  reality  throw  much,  if  any,  new 
light  on  the  subject. 

Liebig  pointed  out  that  universal  experience  teaches 
that  all  organised  bodies  after  death  suffer  a  change,  in 
consequence  of  which  their  remains  gradually  vanish. 
From  the  smallest  twig  to  the  largest  tree  all  vege- 
tables disappear  after  a  few  years,  whilst  animal 
matters  once  deprived  of  life  and  if  exposed  to  the 
air  are  dissipated  in  a  much  shorter  time,  leaving 
only  their  mineral  matter  behind  them.  This  great 
process,  which  requires  for  its  progress  air  and 
moisture,  results  finally  in  the  converting  of  their 
carbon  into  carbonic  acid  gas,  of  their  hydrogen  into 
water,  of  their  nitrogen  into  ammonia,  and  of  their 
sulphur  into  sulphuric  acid.  They  are  then  in  the 
forms  in  which  they  can  serve  as  food  for  new 
generations  of  plants  and  animals.  Those  parts 
which  were  derived  from  the  air  are  returned  to 
the  air,  and  the  mineral  parts  which  were  taken 
from  the  earth  are  returned  once  more  to  the  soil. 
The  death  followed  by  the  dissolution  of  one  genera- 
tion is  the  source  of  life  for  a  succeeding  generation. 
The  atoms  of  carbon  and  hydrogen,  which  yesterday 
formed  part  of  the  brain  or  muscle  of  an  Englishman; 
may  to-morrow  contribute  to  the  material  parts  of  a 


HIS   LIFE    AND   WORK.  67 

Persian  or  a  native  of  Japan.  The  processes  which 
bring  about  these  resolutions  of  organic  matter  into 
the  very  same  simple  bodies  from  which  they  them- 
selves were  formerly  produced,  belong  to  the  class 
which  we  are  considering — to  the  fermentations. 
They  require,  in  order  that  they  may  occur,  moisture, 
and  at  the  earlier  stages  the  presence  of  air ;  after- 
wards, in  many  cases,  fermentations  can  proceed  even 
if  air  be  excluded. 

These  are  the  facts  on  which  Liebig's  theory  of 
the  ferments  was  founded.  Reasoning  upon  them, 
he  said :  "  It  is  obvious  that  by  the  contact  of  these 
organic  compounds  with  the  oxygen  of  the  air,  a 
process  begins,  in  the  course  of  which  their  constituents 
suffer  a  total  change  in  their  properties.  This  change 
is  the  result  of  a  change  in  their  composition.  Before 
contact  with  oxygen,  their  constituents  are  arranged 
together  without  action  on  each  other.  By  the 
oxygen  the  state  of  rest  or  equilibrium  of  the  attrac- 
tions which  keep  the  elements  together  has  been 
disturbecyin  a  particle  of  the  substance,  and,  as  a 
consequence  of  this  disturbance,  a  separation  or  new 
arrangement  of  the  elements  has  been  brought 
about. 

"  The  continuance  of  these  processes,  even  when 
the  oxygen,  the  original  exciting  cause  of  them,  no 
longer  acts,  shows  most  clearly  that  the  state  of  de- 
composition which  has  been  produced  among  the 
elements  of  a  particle  of  the  mass  exerted  an  influence 
on  the  other  particles  which  have  not  been  in  contact 
with  the  oxygen  of  the  air ;  for  not  only  the  first 
particles,  but,  by  degrees,  all  the  rest  undergo  the  same 
change. 

"  All  those  processes  of  decomposition,"  he  con- 


68  JUSTUS  voN  LIEBIG: 

tinues,  "  which  begin  in  a  part  of  an  organic  substance 
from  the  application  of  an  external  cause,  and  which 
spread  through  the  whole  mass,  with  or  without  the 
co-operation  of  that  cause,  have  been  called  processes 
of  putrefaction.  A  putrescible  substance,  therefore, 
is  distinguished  from  one  not  putrescible,  because  the 
former,  without  other  conditions  than  a  certain  tem- 
perature, and  the  presence  of  water  (after  exposure, 
although  transient,  to  the  atmosphere),  are  resolved 
into  a  series  of  new  products,  while  the  latter,  if  un- 
mixed, do  not,  under  the  same  circumstances,  undergo 
any  change." 

The  number  of  substances,  however,  which  are  thus 
putrescible  is  few,  though  they  are  widely  diffused. 
They  are  all  of  them  highly  complex,  containing 
nitrogen  and  sulphur — such  things  as  albumin,  fibrin, 
and  gelatin,  for  example. 

On  the  other  hand,  a  great  number  of  substances, 
such  as  sugar,  starch,  and  the  organic  acids  which  are 
found  in  the  juices  of  plants,  are  not  putrescible  if 
pure;  if  exposed  to  air  and  moisture,  they  do  not 
undergo  any  perceptible  change ;  a  solution  of  sugar, 
for  example,  when  exposed,  dries  up  and  deposits 
crystals  which  retain  their  original  properties. 

If,  however,  some  sugar,  or  sugar  of  milk,  &c.,  be 
dissolved  in  water,  and  if  the  solution  be  added  to  a 
portion  of  a  putrescible  substance  already  in  a  putrid 
condition,  these  substances  will  then  be  fermented, 
that  is  to  say,  will  undergo  a  change. 

Substances  like  sugar  and  starch  were  termed  by 
Liebig  the  fermentescible  substances.  The  process 
of  their  decomposition  under  the  influence  of  the 
putrescible  substances,  according  to  him,  is  what  we 
call  fermentation.  And  it  will  be  perceived  by  this 


HIS    LIFE    AND    WORK.  69 

time  that  the  putrescent  matters  which  can  thus 
induce  the  decomposition  of  the  "  fermentescible " 
substances  are  the  ferments. 

If  one  examines  the  juices  of  vegetables,  or  fluids 
of  animal  origin,  one  finds  present  in  them  always, 
in  greater  or  less  quantity,  the  instable  compounds  of 
the  first  class  (Liebig's  ferments) ,  as  well  as  substances 
of  the  second  class.  This  fact  explains,  according  to 
Liebig's  hypothesis^  why  all  such  juices  undergo  fer- 
mentation after  contact  with  air,  in  the  course  of  which 
they  are  ultimately  reduced  to  substances  of  simpler 
composition  than  before. 

The  products  of  a  fermentation  are,  as  we  know, 
commonly  of  more  simple  composition  than  the 
substances  from  which  they  are  derived.  Thus, 
grape  sugar,  which  has  the  formula  C6H1::>06,  when 
fermented  yields  chiefly  alcohol,  C2H60,  and  carbonic 
acid  gas.  Sugar  of  milk  may  similarly  be  made  to 
yield  a  simpler  compound — lactic  acid.  In  order 
that  such  changes  as  these  may  occur,  it  seemed 
obvious  that  the  atoms  of  the  substance  fermented 
must  be  set  in  motion,  since,  in  order  to  rearrange 
themselves,  it  is  plain  that  they  must  move.  From 
this  Liebig  concluded  that  the  power  of  the  ferments 
over  fermentable  substances  depends  on  a  certain  state 
or  condition  of  their  atoms,  and,  further,  that  this 
state  must  be  one  in  which  the  complex  molecules 
of  the  ferments  undergo  resolution  into  simpler 
molecules.  Thus,  the  action  of  a  ferment  on  a 
fermentable  compound,  seemed  to  Liebig  not  unlike 
that  of  heat  on  an  organic  compound.  In  virtue  of 
the  motions  of  the  atoms  of  its  own  molecules,  it 
disturbs  the  equilibrium  previously  existing  among 
the  atoms  of  the  molecules  of  the  fermented  matter, 


70  JUSTUS   VON   LIEBIG: 

and  new  and  simpler  combinations  result.  This 
analogy  he  found  to  be  confirmed  by  the  influence 
of  temperature  on  fermentation.  If  an  organic 
substance  be  submitted  to  a  given  temperature 
certain  definite  products  are  obtained,  which  may, 
however,  be  altered  if  a  higher  temperature  be 
employed.  Similarly,  the  products  of  fermentations 
are  markedly  influenced  by  the  temperatures  at 
which  the  fermentations  occur. 

But,  it  will  be  asked,  what  is  it  that  starts  these 
internal  movements,  which  changes  a  merely 
putrescible  substance  into  an  actually  putrescent 
body  or  ferment  ? 

Liebig  was  of  opinion  that  the  oxygen  of  the  air 
was  the  first  cause  of  the  breaking-up  of  the  nitro- 
genous substances.*  The  immediate  and  most 
energetic  cause  of  all  the  alterations  and  transfor- 
mations which  organic  molecules  undergo  is,  he 
says,  "  the  chemical  action  of  oxygen."  That  is  why 
exposure  to  the  air  is  a  necessary  preliminary 
condition  for  the  commencement  of  a  fermentive 
change. 

Fermentation,  according  to  Liebig,  is  only  a 
consequence  of  the  commencement  of  a  process  of 
decay,  in  which  oxygen  plays  a  part,  and  it  continues 
till  the  fermenting  substance  has  resolved  itself  into 
a  series  of  new  products  which  undergo  no  further 
change,  unless  as  the  result  of  further  causes  ot 
alteration. 

But  although  a  state  of  rest  may  thus  be  reached 
in  regard  to  the  attractions  among  the  atoms  of  the 
newly-formed  substances,  yet  this  condition  of 
equilibrium  would  not  exist  with  regard  to  their 

*  Familiar  letters. 


HIS    LIFE    AND    WORK.  71 

attraction  for  oxygen.  The  chemical  action  of  oxygen 
would  only  cease  when  the  capacity  of  the  elements 
to  combine  with  oxygen  was  exhausted.  Fermenta- 
tion, therefore,  represents  only  the  first  stage  of  the 
resolution  of  complex  molecules  into  simpler  ones. 
The  process  is  completed  by  decay,  which  he  defined 
as  "  a  process  of  combustion  taking  place  at 
common  temperatures,  in  which  the  products  of  the 
fermentation  and  putrefaction  of  plants  and  of 
animal  bodies  combine  gradually  with  the  oxygen  of 
the  atmosphere,"  producing  carbonic  acid,  water,  and 
ammonia. 

There  are  many  compounds  which,  by  themselves, 
are  deficient  in  the  property  of  absorbing  oxygen. 
Alcohol,  for  example,  only  combines  with  oxygen  at 
a  comparatively  high  temperature.  For  such  things 
contact  with  a  substance  itself  undergoing  change 
was  held  by  Liebig  to  be  the  chief  condition  of  decay. 
They  then  behave,  he  said,  as  if  they  were  a  part  of 
the  decaying  material,  and  their  oxidation  is  effected. 
He  offered  as  an  instance  the  German  "  quick  vinegar 
process,"  in  which  alcohol,  in  the  form  of  wine  or 
diluted  brandy,  is  allowed  to  flow  slowly  over  shavings 
of  wood,  packed  in  casks  through  which  a  slight 
current  of  air  also  circulates.  The  alcohol,  in  spite 
of  its  want  of  attraction  for  oxygen  is,  under  these 
circumstances,  quickly  converted  into  vinegar.  This 
would  not,  however,  occur  if  pure  spirit  were  passed 
over  a  non-putrescible  material,  and  at  the  com- 
mencement of  the  process  it  is  usual  to  add  to  the 
spirit  a  small  quantity  of  one  of  those  substances 
which  are  capable,  unassisted,  of  undergoing  decay — 
such  as  beer- wort,  honey,  vinegar —  then,  after  the  lapse 
of  a  short  time,  the  surface  of  the  shavings  passes, 


72  JUSTUS   VON   LIEBIG: 

according  to  this  view,  into  a  state  of  oxidation,  and 
from  that  time  there  is  no  further  need  of  the 
co-operation  of  added  decaying  matter. 

Such  was  Liebig's  explanation  of  the  phenomena 
of  fermentation  and  decay. 

But  not  even  the  authority  of  a  Liebig  will  for 
long  protect  a  wide-reaching  hypothesis,  such  as  this, 
from  criticism,  and  soon  its  great  rival,  the  vitalistic 
theory  of  fermentation,  was  revived  by  Louis  Pasteur, 
who  brought  to  its  support  observations  and  new  facts 
of  a  most  startling  character. 

The  starting-point  of  the  vitalistic  theory  of  fer- 
mentation is  to  be  found  in  the  observation  made  in 
1680,  by  Leuwenhoeck,  when  examining  beer  yeast 
with  the  microscope,  that  this  substance  consists  of 
small  globules,  which  are  spherical  or  globular  in 
form,  but  whose  nature  he  was  not  able  to  deter- 
mine. A  century  and  a  half  later  the  observations  of 
Cagniard  de  Latour,  and  soon  afterwards  those  of 
Schwann,  at  Jena,  and  Klitzing,  at  Berlin,  showed  that 
yeast  consists  of  a  mass  of  organic  globules  capable 
of  reproducing  themselves  by  buds ;  these  globules 
seemed  to  them  to  belong  to  the  vegetable  kingdom, 
and  not  to  be  simply  organic  chemical  compounds,  as 
had  till  then  been  supposed  to  be  the  case.  They 
concluded  that  probably  the  converting  of  sugar  into 
alchohol  and  carbon  dioxode  was  an  effect  of  their 
vegetative  processes.  This  view  of  the  action  of  yeast 
cells  was  not,  however,  widely  accepted  till  it  had  the 
support  of  Pasteur's  experiments,  and  not  universally, 
even  then,  until  after  a  controversy  of  the  keenest 
kind. 

Liebig  did  not  deny  the  organised  nature  of  yeast, 
nor  its  power  of  multiplication  by  budding,  but  he 


HIS    LIFE    AND   WORK.  73 

was  of  opinion  that  the  living  cells  are  always  accom- 
panied, also,  by  dead  cells,  and  that  it  was  the  mole- 
cular motions  of  the  decaying  matter  of  these  dead 
cells  which  was  communicated  to  the  sugar  and 
brought  about  its  decomposition  by  fermentation. 

To  put  this  idea  to  the  test  of  experiment,  Pasteur, 
who  was  not  one  whit  behind  Liebig  himself  in  his 
conviction  that  experiment  is  the  final  court  of  appeal 
on  all  scientific  questions,  sowed  almost  imponderable 
portions  of  fresh  yeast  cells  in  solutions  of  pure  sugar, 
to  which  he  had  added  small  quantities  of  such 
mineral  salts  as  are  necessary  for  their  growth,  with  the 
result  that  the  cells  thus  sown  multiplied,  and  the  sugar 
fermented  as  before.  From  this  result  he  concluded 
that  the  process  mainly  took  place  between  the  sugar 
and  a  ferment  germ,  which  owed  its  life  and  develop- 
ment to  the  nutritive  matter  he  supplied  to  it.  The 
most  important  of  these  nutritive  substances  was  the 
sugar.  That  fermentation,  in  short,  is  simply  a  pheno- 
menon of  nutrition,  in  which  the  organism  assimilates 
one  part  of  the  fermentable  matter,  using  it  for  its 
growth  and  for  the  production  of  new  individuals,  and 
converts  the  rest  into  the  well-known  products  of  the 
change.  This  attempt  at  a  crucial  experiment  by 
means  of  the  fermentation  of  pure  sugar,  in  associa- 
tion with  mineral  salts,  does  not,  by  itself,  as  a  close 
examination  shows,  really  finally  overthrow  Liebig's 
hypothesis,  for  it  is  manifestly  reasonable  to  sup- 
pose, first,  that  even  the  small  amount  of  ferment 
taken,  however  carefully  purified,  must  have  been 
accompanied  by  a  certain  amount  of  what  Liebig 
called  putrescible  material ;  and,  secondly,  that 
the  growth  and  life  of  the  yeast  would  be  soon 
accompanied  by  the  death  of  some  part  of  it.  This 


74  JUSTUS   VON    LIEBIG: 

would  supply  the  putrescible  matter  even  if  it  were 
absent  in  the  first  instance. 

It  is  scarcely  surprising,  therefore,  that  Liebig  was 
not  for  some  time  convinced  of  the  dependence 
of  fermentation  on  the  existence  of  these  organisms 
by  the  facts  brought  forward  by  his  opponent ;  and  he 
made  merry  over  these  minute  beings  which  feed  on 
sugar,  and  secrete  alcohol,  whose  appearance  simul- 
taneously with  the  fermenting  of  the  sugar,  had  been 
held  to  support  the  idea  that  fermentation  is  a  result 
of  their  vital  processes.  To  him  the  presence  of 
animalculso  in  putrefying  matter  appeared  to  be  of  the 
nature  of  an  accident,  their  number,  when  large, 
being  the  result  of  the  fact  that  these  organisms  find 
in  such  matters  the  most  favourable  conditions  for 
their  nutrition  and  development,  their  presence  being 
often  very  beneficial,  since  it  resulted  in  a  more  rapid 
oxidation  of  the  material  concerned.  Fortunately  for 
science,  Pasteur  did  not  confine  himself,  as  his  pre- 
decessors had  done,  to  the  investigation  of  a  single 
case  of  fermentation.  He  carried  his  researches 
into  other  fields,  and  thereby  enriched  science  with 
many  new  facts,  some  of  which  are  of  incalculable 
importance,  in  consequence  of  the  light  they  have 
thrown  on  the  nature  of  several  of  the  most  virulent 
diseases  by  which  animals  and  men  are  afflicted, 
and  because  they  stimulated  other  observers  to  make 
equally  productive  exertions  in  many  new  directions. 

When  Liebig's  earliest  opinions  were  formed  on 
the  subject  of  fermentation,  only  the  fermentation  of 
sugar  by  yeast  had  received  any  considerable  atten- 
tion on  its  biological  side,  but  subsequently  Pasteur 
extended  the  range  of  his  investigations,  and  was  able 
to  connect  the  existence  of  other  organisms  with 


HIS    LIFE    AND    WORK.  75 

other  fermentive  changes.  Thus  he  found  that  the 
lactic  fermentation,  in  which  sugar  of  milk  pro- 
duces lactic  acid,  is  associated  with  the  growth  of 
a  grey  substance  which  may  be  easily  overlooked, 
partly  because  the  amount  produced  is  usually  re- 
latively small,  partly  on  account  of  the  difficulty  of 
distinguishing  it  from  the  other  materials  present. 

The  grey  matter  in  question,  when  separated  from 
other  substances,  appears,  as  seen  under  the  micro- 
scope, to  be  formed  of  small  globules  or  points  smaller 
than  those  of  beer  yeast.  Pasteur  showed  a  fairly 
complete  analogy  between  the  known  facts  relating 
to  these  two  fermentations,  and  proved  further,  that 
whilst  in  the  presence  of  both  ferments  both  fermenta- 
tions can  proceed  under  suitable  conditions,  lactic  acid 
is  never  produced  in  normal  alcoholic  fermentation. 

Vinegar,  as  has  previously  been  explained  (p.  71), 
is  produced  by  exposing  wine  or  diluted  brandy  to 
the  air  ;  oxygen  is  absorbed  by  the  alcohol  present  in 
these  liquids,  and  the  alcohol  is  thereby  converted 
into  acetic  acid.  Pure  alcohol  will  not  undergo 
this  oxidation;  it  is  necessary,  as  will  be  remem- 
bered, to  add  a  little  beer- wort,  meat-juice,  or  some 
such  putrescible  body,  in  order  that  "acetic  fer- 
mentation" shall  set  in.  It  is  necessary,  in  fact, 
to  have  a  "  ferment,"  and  Liebig,  as  we  know,  be- 
lieved the  ferment  to  be  nitrogenous  matter  in  a 
state  of  change.  Pasteur,  on  the  other  hand,  attri- 
buted the  acetous  fermentation  to  a  plant,  which 
had  long  been  known  under  the  name  of  "flower 
of  vinegar,"  a  little  fungus  which  floats  on  the 
surface  of  wine  during  the  process  which  transforms 
it  into  vinegar.  The  yeast  plant  sometimes  forms  a 
hardly  visible  veil  over  the  surface  of  the  liquid,  at 


76  JUSTUS   VOX   LIEBIG: 

others  it  exists  as  a  wrinkled  film,  very  thin  and 
unctuous  to  the  touch.  This  little  organism,  which 
can  only  exist  if  it  be  plentifully  supplied  with  its 
proper  aliments  and  at  a  moderate  temperature, 
possesses,  Pasteur  contended,  the  power  of  condensing 
considerable  quantities  of  oxygen  from  the  air  and  of 
fixing  this  gas  on  alcohol.  It  is  one  of  those  so-called 
spontaneous  productions  which,  like  moulds,  almost 
always  make  their  appearance  on  liquids  suitable  for 
their  growth;  they  or  their  germs  appear  to  exist 
everywhere  around  us,  so  that  if  one  wants  them  it  is 
generally  only  necessary  to  expose  a  suitable  nutrient 
liquid — in  this  case  a  mixture  of  wine  and  vinegar 
will  do  well — in  a  warm  place,  and  they  will  soon 
make  their  appearance. 

Pasteur  showed  that,  owing  to  the  sensitiveness  of 
the  vinegar  plant,  it  is  destroyed  by  a  temperature  of 
a  little  above  60°  C.,  and  that  wine  heated  to  that 
temperature,  even  if  afterwards  exposed  to  filtered  air, 
refuses  to  become  vinegar.  This  temperature,  he 
argued,  must  have  left  intact  the  albuminous  and 
nitrogenous  substances  in  the  wine,  and  hence  these 
cannot  be  regarded  as  the  source  of  the  fermentation ; 
in  short,  the  ferment  in  this  case  must  be  the  living 
vinegar  plant. 

Such  experiments  as  those  which  have  been  quoted, 
and  perhaps  still  more  the  constant  connection  which 
has  been  shown  by  Pasteur  and  others  to  exist  between 
certain  fermentive  diseases  and  definite  organisms, 
have  now  for  some  time  past  satisfied  nearly  everyone 
that  fermentation,  including  in  that  term  also  putre- 
faction and  decay,  is,  as  Pasteur  has  so  vehemently 
insisted,  in  many  cases  connected  with  the  existence 
of  organisms,  and  that  each  kind  of  fermentation  is 


HIS    LIFE   AND   WORK.  77 

dependent  on  the  growth  and  development  of  a 
particular  organism.  To  this  very  considerable 
extent  Pasteur  has  fixed  the  vitalistic  theory  on 
so  secure  a  base,  that  even  Liebig  practically  ad- 
mitted its  truth  in  his  later  writings.  And  yet,  in 
spite  of  the  success  of  the  vitalistic  theory,  it  cannot 
be  said  that  this  theory  has  overthrown  its  rival 
Although  the  connection  of  many  fermentations  with 
the  life  of  definite  organisms  has  been  clearly  proved, 
there  remain  a  number  of  changes,  which  may  also  be 
described  as  fermentations,  the  occurrence  of  which, 
it  seems  almost  certain,  does  not  depend  upon  such 
organisms.  And,  besides,  though  it  is  clear  that  hi 
many  cases  fermentation  depends  on  the  presence 
of  micro-organisms,  we  do  not  yet  know  how  these 
organisms  act.  We  do  not  know  whether  they  live 
on  the  fermentable  matter  and  excrete  the  products 
of  the  fermentation,  or  whether  the  microbes  produce 
soluble  ferments,  such  as  will  be  presently  mentioned, 
which  afterwards  bring  about  the  fermenting  of  the 
fermentable  substances  in  some  manner  more  or  less 
like  that  which  Liebig  suggested.  As  regards  the 
first  alternative,  it  may  be  pointed  out  that  the 
amount  of  the  products  of  a  fermentation  is  usually 
very  great,  in  proportion  to  the  mass  of  the 
organisms  concerned  and  to  the  time  they  are  in 
action.  On  the  other  hand,  as  regards  the  second 
alternative,  though  attempts  to  isolate  soluble 
ferments  from  the  organisms  have  not  often  been 
successful,  yet  it  has  been  done.  Hence,  a  priori, 
there  is  nothing  improbable  in  the  second  suggestion, 
as  the  past  failure  to  isolate  these  substances  may 
well  have  been  due  to  want  of  knowledge  and  experi- 
ence. The  difficulty  is  always  to  begin. 


78  JUSTUS  VON   LIEBIG: 

This  brings  us  again  to  the  further  important  fact, 
that  besides  the  organised  ferments  whose  existence 
was  established  by  Pasteur  and  others,  there  are  yet 
other  ferments  of  quite  a  different  nature ;  such  are 
the  active  agent  (emulsin)  in  the  change  by  which 
the  amygdalin  of  bitter  almonds  yields  sugar,  prussic 
acid,  and  oil  of  bitter  almonds  (see  p.  35),  and  the 
ptyalin  of  saliva,  by  which  starch  may  be  transformed 
into  a  sugar.  These  latter  ferments  are  called  enzymes. 
They  are  believed  to  be  unorganised  chemical  sub- 
stances which  result  from  the  activity  of  living  cells. 
The  changes  which  they  bring  about  are  analogous  to 
those  induced  by  the  organised  ferments  themselves. 
Like  the  latter,  they  appear  to  be  independent  of 
any  change  in  the  agent  which  produces  them, 
and  in  both  cases  great  effects  are  produced  by 
what  seem  to  us,  at  first  sight,  very  trivial  causes. 
Whilst  Liebig  was  wrong  in  denying  the  existence 
of  any  connection  between  the  organisms  and  the 
fermentations,  it  must  be  admitted,  on  the  other 
hand,  that  his  opponents  have  not  yet  succeeded  in 
explaining  their  mode  of  action,  so  that  it  is  not 
impossible  that  some  modification  of  the  theory  of 
Liebig  may  yet  be  found  useful.  The  rival  theories  of 
fermentation  which  have  here  been  discussed  have 
jointly  and  severally  done  a  splendid  work,  by 
stimulating  and  guiding  workers  in  this  field  of 
science,  from  which  rich  crops  have  already  been 
gathered,  and  which  seems  to  promise  results  in  the 
future,  such  as  the  earlier  workers  would  scarce  have 
dared  to  dream  of  when  they  began  their  labours. 

It  now  seems  possible  that  the  difference  between 
an  organised  and  an  unorganised  ferment  may  be 
this — that  the  active  agent  of  the  organised  ferment 


HIS    LIFE   AND   WORK.  79 

is  one  which  only  acts  within  the  cells  in  which 
it  is  formed,  and  which  has  not  yet,  with  one  or 
two  exceptions,  been  separated  from  the  cells  which 
contain  it ;  whilst  the  unorganised  ferments  are  those 
which  can  act  outside  the  cells  which  produce  them. 

Whatever  may  be  the  final  fate  of  Liebig's  theory 
of  the  ferments,  I  fear  it  must  be  said,  after  nearly 
half  a  century  of  interesting,  active  work,  that  it  has 
not  yet  been  replaced  by  a  really  general  and  satis- 
factory hypothesis. 


80  JUSTUS   VON   LIEBIG: 


CHAPTER    VI. 

CHEMISTRY   OF  AGRICULTURE. 

Commemorative  Addresses — Components  of  Plants — Relations  of 
Plants  and  Animals—  Davy's  Lectures—  Boussingault's  Labora- 
tory— The  Humus  Theory — Opinions  in  Germany  and  England 
—  Overthrow  of  Humus  Theory — Evidence  that  Air  is  Source 
of  Carhon  of  Vegetables — Plants  Source  of  Carbon  for  Animals 
— The  Real  Use  of  Humus — Sources  of  Components  of  Plants 
Other  than  Carbon — Origin  of  Nitrogen  of  Plants — Mineral 
Theory  of  Manures — Liebig's  Experiments  in  Agriculture — 
Errors  Made  in  Applying  the  Mineral  Manures,  and  how  they 
were  Corrected — "  Ground  Absorption  "  of  Soils — Object  of 
Liebig's  Practical  Work  in  Husbandry — "  The  Natural  Laws 
of  Husbandry  " — Deterioration  of  Land  in  Western  Countries  ; 
How  to  Avoid  it — Liebig's  Influence  on  Education  of  Agri- 
culturists. 

SPEAKING  generally,  the  first  twenty  years  of  Liebig's 
life,  after  his  return  from  Paris,  were  devoted  to 
pure  chemistry.  The  next  period  was  distinguished 
by  his  remarkable  contributions  to  chemistry  as 
applied  to  agriculture  and  physiology.  Perhaps  some 
idea  of  the  range  and  depth  of  his  work  over  the  whole 
field  of  pure  and  applied  chemistry  may  be  gained 
from  the  fact  that,  on  his  death,  in  1873,  it  was  felt 
to  be  impossible  that  any  one  man  could  sufficiently 
comprehend  all  the  subjects  he  had  advanced  and  his 
share  in  their  advancement,  and  that,  therefore,  not 
one,  but  three  of  his  colleagues,  all  men  of  great  emi- 
nence, were  charged  with  the  duty  of  delivering 
commemorative  addresses,  each  one  of  them  under- 
taking that  part  of  the  great  master's  work  with  which 


HIS    LIFE   AND   WORK.  81 

he  was  himself  most  familiar  from  his  own  life-work. 
(See  p.  9.) 

Liebig's  first  writings  on  agricultural  chemistry 
and  on  fermentation  were  presented  in  1840  *  to  the 
Members  of  the  British  Association,  as  part  of  a 
Report  upon  the  Present  State  of  Organic  Chemistry, 
in  fulfilment  of  a  task  which  had  been  imposed  upon 
him  by  its  chemical  section  at  a  previous  meeting. 
From  the  work  which  he  then  began,  in  response 
to  the  duty  thus  laid  upon  him,  he  may  be  said 
never  to  have  withdrawn  his  hand.  The  subject 
was  worthy  of  the  worker.  "  Perfect  agriculture,"  as 
he  says,  in  his  preface  to  this  book,  "  is  the  true 
foundation  of  all  trade  and  industry,  it  is  the  founda- 
tion of  the  riches  of  states.  But  a  rational  system  of 
agriculture  cannot  be  formed  without  the  application 
of  scientific  principles,  for  such  a  system  must  be 
based  on  an  exact  acquaintance  with  the  means  of 
nutrition  of  vegetables,  and  with  the  influence  of  soils 
and  actions  of  manure  upon  them.  This  knowledge 
we  must  seek  from  chemistry,  which  teaches  the 
mode  of  investigating  the  composition,  and  of  studying 
the  character  of  the  different  substances  from  which 
plants  derive  their  nourishment.  .  ." 

These  were  the  convictions  which  impelled  Liebig 
to  bring  his  unique  and  now  highly- trained  faculties  to 
bear  on  the  task  of  creating  a  science  of  agriculture, 
and  to  enter  a  field  which  had  lain  fallow  since  the  time 
of  Davy,  who  was  the  first  chemist  to  occupy  himself 
with  the  study  of  the  application  of  chemical  principles 
to  the  growth  of  vegetables  and  to  organic  processes. 

*  Liebig's   "Chemistry  in  its  Applications  to  Agriculture  and 
Physiology."      Published   in-  Brunswick,     1840.      English    Edition 
Edited  by  Dr.  Lyon  Playfair,  London,  1840. 
F 


82  JUSTUS   VOX    LIEBIG: 

When  Liebig  began  this,  his  second  great  work, 
he  was  not  far  from  the  zenith  of  his  career. 
No  one  was  better  trained  than  he  in  the  methods 
of  organic  analysis,  which  he  had  brought  to  per- 
fection and  applied  to  their  purpose,  as  Wohler  says, 
with  almost  pedantic  exactness.  He  was  surrounded, 
too,  by  a  number  of  pupils  eager  and  well  qualified 
to  aid  him  in  his  undertaking ;  among  them  at  this 
moment  was  Lyon  Playfair,  to  whom  was  entrusted 
the  duty — well  carried  out — of  editing  Liebig's  first 
book,  for  publication  in  England. 

Liebig's  first  book  on  chemistry,  in  its  applications 
to  agriculture  and  vegetable  physiology,  quickly 
passed  through  a  number  of  editions.  Twenty-two 
years  later,  after  he  had  studied  in  minute  detail 
the  various  questions  involved  in  this  subject,  and 
taken  part  in  numerous  discussions  with  agriculturists 
and  others,  at  home  and  abroad,  he  published  an  em- 
bodiment of  his  researches  in  "  The  Natural  Laws  of 
Husbandry,"  a  work  which  has  been  truly  described 
by  Hofmann  as  the  first  perfect  construction  of  the 
philosophy  of  agriculture  Avhich  had  ever  appeared 
up  to  that  date.  This  work  was  originally  issued  in 
two  parts.  The  second  part  was  published  in  an 
English  translation  under  the  above  title. 

Liebig  spared  no  pains  in  order  to  qualify  him- 
self on  the  technical  side  for  this  new  undertaking. 
Besides  studying  the  practice  of  husbandry  at 
home,  he  paid  a  visit  to  Great  Britain,  and  made 
a  journey  through  the  agricultural  districts  of 
England  and  Scotland,  in  order  that  he  might 
acquaint  himself  personally  with  the  various 
practices  of  different  districts  in  farming,  in  butter- 
making  in  cheese-making,  and  so  on. 


HIS    LIFE    AND   WORK.  83 

Side  by  side  with  his  labours  on  behalf  of 
agriculture,  Liebig  undertook  another  and  equally 
searching  investigation  into  the  applications  of 
chemistry  to  physiology  and  pathology.  It  was  a 
happy  inspiration  which  led  him  to  combine 
in  his  researches  these  two  lines  of  work,  each  so 
important  to  the  welfare  of  mankind,  each  so 
closely  bearing  upon  the  other.  The  study  of  agri- 
culture, consists  largely  in  the  study  of  the  science 
of  manuring.  Liebig's  strict  investigation  of  the 
processes  of  nutrition  in  the  animal  organism,  and  of 
the  origin  of  animal  excrements,  enabled  him  in 
the  end  to  understand,  better  than  those  who 
preceded  him,  the  cause  of  the  beneficial  effects  of 
these  excrements  on  the  growth  of  vegetables,  and 
enabled  him  to  trace  among  the  multitudinous 
phenomena  of  life  processes,  a  few  simple  yet  funda- 
mental laws  for  the  guidance  of  practical  farmers. 

Interesting  as  it  would  be  to  follow  the  details  of 
Liebig's  agricultural  investigations  during  the  years 
of  his  chief  activity  in  this  direction,  it  is  impossible 
to  attempt  it.  Were  we  to  do  so,  we  should  see 
him  now  at  his  desk,  now  working  in  his  laboratory, 
now  guiding  the  older  students  in  their  share  of  his 
studies  ;  at  another  time  we  should  have  to  follow 
him  to  the  factory,  where  his  mineral  manures  were 
prepared;  then  go  with  him  to  his  experimental 
plot  to  watch  their  effects ;  or  accompany  him  to 
some  gathering  of  agriculturists,  scientific  or  other- 
wise, to  join  in  discussions,  which  were  often  warm 
and  always  animated,  on  the  agricultural  topic  of 
the  moment.  In  no  part  of  all  these  varied  duties 
did  Liebig  fail  to  take  his  full  share.  The  work 
of  the  porter  in  the  manure  factory,  that  of  the 


<S4  JUSTUS    VON    LIEBIG  : 

labourer  on  the  farm,  and  of  the  student  at  his  analysis 
was  all  done  under  his  close  guidance,  and  was  as 
fully  the  outcome  of  his  inspiration  as  that  part 
which  was  done  with  his  own  hands  and  head 
alone.  But,  delightful  as  it  would  be  thus  closely 
to  watch  the  activities  of  such  a  man,  all  that  can 
be  even  attempted  is  to  try  to  gain  a  clear  view 
of  the  ideas  which  animated  Liebig's  work  at  its 
inception,  of  the  main  features  of  the  labours  he 
undertook,  of  the  difficulties  he  met  and  overcame, 
and,  finally,  of  the  position  to  which  agricultural 
science  had  been  raised  when  these  labours  were 
brought  to  a  conclusion. 

For  the  benefit  of  the  uninitiated,  it  must  here 
be  pointed  out,  that  there  is  a  beautiful  connection 
between  the  organic  and  the  inorganic  kingdoms  of 
nature.  It  is  inorganic  matter  mainly  which  affords 
food  to  plants,  and  they,  on  the  other  hand,  yield  the 
means  of  subsistence  to  animals. 

The  conditions  necessary  for  animal  and  veget- 
able nutrition  are  essentially  different.  An  animal 
requires  for  its  development,  and  for  the  sustenance 
of  its  vital  functions,  a  certain  class  of  substances 
which  can  be  generated  only  by  certain  organic 
beings  possessed  of  life — viz.  by  the  plants. 
Although  many  animals  are  entirely  carnivorous, 
yet  their  nourishment  is  ultimately  derived  from 
plants,  for  the  animals  on  which  the  carnivora 
feed  receive  their  nutriment  from  vegetable  mat- 
ter. Plants,  on  the  other  hand,  find  new  nutritive 
material  only  in  inorganic  substances.  Hence,  one 
great  end  of  vegetable  life  is  to  generate  matter 
adapted  for  nourishing  the  animals  out  of  inorganic 
substances  which  are  not  fitted  for  that  purpose. 


HIS    LIFE    AND   WORK.  85 

These  are  almost  the  very  words  with  which  Liebig 
opened  his  book  on  "  Chemistry  in  its  Appli- 
cation to  Vegetable  Physiology  and  Agriculture." 
He  devoted  the  first  part  of  this  book  to  an 
examination  of  the  matters  which  supply  nutriment 
to  plants,  and  of  the  changes  which  these  undergo 
in  the  living  organism. 

The  second  part  of  the  book  deals  with  fermenta- 
tion, putrefaction,  and  decay ;  but  this  department  of 
Liebig's  work  has  already  come  before  us. 

All  parts  of  all  plants  contain  carbon  and  hydrogen ; 
these  are  among  the  constituents  of  all  their  organs ; 
they  are  absolutely  essential  to  their  existence. 

The  substances  of  which  the  greater  part  of 
vegetables  are  composed  also  contain  oxygen ;  the 
larger  part  of  these  substances  are  compounds  in 
which  carbon  is  present,  together  with  hydrogen  and 
oxygen  in  the  proper  proportions  for  forming  water. 
Sugar,  starch,  gum,  and  the  materials  of  which  the 
outer  walls  of  plants  are  formed  are  all  of  this  character ; 
such  substances  are  called  by  chemists  carbohydrates. 
Other  oxidised  substances  also  occur,  in  which  the 
proportion  of  oxygen  is  greater ;  many  of  these  are 
sour  bodies,  such  as  the  vegetable  acids.  Wax,  resin, 
and  the  fixed  oils  usually  contain  these  three  elements, 
but  in  their  case  oxygen  is  either  absent  or  is  present 
in  smaller  proportion  than  that  which  is  found  in  the 
carbohydrates. 

Besides  this,  the  juices  of  plants  contain  small 
quantities  of  mineral  matter  which  may  be  detected 
in  their  ashes,  whilst  nitrogen  is  present,  especially 
in  the  seeds.  The  proportion  of  nitrogen  is  small,  but 
it  is  rarely  altogether  absent  from  any  part  of  a  plant ; 
it  is  a  component  of  such  substances  as  the  gluten  of 


86  JUSTUS   VON   LIEBIG: 

wheat,  vegetable  albumen,  and  of  the  alkaloids,  such 
as  quinine  and  strychnine.  Finally,  plants  also  con- 
tain a  little  sulphur  and  phosphorus. 

From  these  facts  it  follows  that  the  nourishment 
of  a  plant  must  contain  carbon,  nitrogen,  phosphorus, 
and  sulphur  in  forms  suitable  for  their  assimilation. 
Water  and  mineral  matter  must  also  be  supplied  to  it. 

From  what  sources  are  these  obtained  ?  Which  of 
them,  if  any,  come  from  the  air,  which  from  the  soil  ? 
Are  the  sources  of  supply  exhaustible  or  inexhaustible, 
practically  speaking  ?  Does  nature  provide  modes  of 
replenishing  the  supplies  of  all  or  any  of  them  ?  How 
far  do  the  lives  of  animals  and  the  arrangements  of 
mankind  supplement  or  oppose  themselves  to  such 
replenishment  ?  If  the  latter  tend  to  exhaust  the 
supply  of  any  constituent  or  constituents,  how  can 
these  arrangements  be  modified  so  as  to  prevent  this, 
or,  better,  so  as  to  produce  enrichment  in  place  of 
exhaustion  ?  These  are  some  of  the  great  questions 
for  the  agriculturist  and  the  agricultural  chemist. 

How  can  we  educate  the  agriculturist  and  the 
man  of  science,  so  that  they  shall  face  these  problems 
with  an  open  mind,  and  co-operate  in  attempting  to 
solve  these  and  similar  questions  ?  This  is  one  of  the 
great  problems  of  technical  education ;  considering 
the  vital  importance  of  agriculture,  it  is  perhaps  the 
great  question  of  technical  education. 

It  was  said  above  that  Liebig  first,  after  Davy, 
attempted  to  construct  a  theory  of  agricultural 
chemistry;  but  it  should  be  mentioned  that  very 
shortly  after  the  commencement  of  Davy's  work,  De 
Saussure  published  his  "  Chemical  Researches  on 
Vegetation,"  and  that  from  1834  Boussingault  also 
worked,  with  devotion,  at  agricultural  chemistry. 


HIS    LIFE   AND   WORK.  87 

The  results  these  two  investigators  published  are 
frequently  referred  to  by  Liebig  in  the  course  of  his 
writings,  and  there  is  no  doubt  at  all  that  the  data 
they  supplied  contributed  very  largely  to  form  the 
basis  of  Liebig's  historic  generalisations. 

The  foundations  of  the  chemistry  of  agriculture 
were  of  necessity  laid  somewhat  late,  for,  from  what 
has  been  said,  it  will  be  seen  that  it  was  impossible  to 
gain  any  true  conceptions  on  the  subject  until  an 
accurate  knowledge  of  the  composition  of  air  and 
water  had  been  attained. 

When  Liebig  commenced  the  studies  which  ended 
in  the  overthrow  of  the  humus  theory,  the  composi- 
tion of  the  air,  of  water,  and  of  carbonic  acid  gas  were 
known.  The  importance  of  minerals  to  plants  was 
admitted,  and  the  advantage  of  adding  them,  in 
the  form  of  marl  to  manure  had  been  suggested, 
more  than  a  century  earlier,  but  their  mode  of 
action  was  still  under  discussion.  Thaer,  the  agri- 
culturist, regarded  thein  as  non-essential,  or  at  best 
useful  as  a  kind  of  stimulant,  whilst  De  Saussure  and 
Davy  were  opposed  to  this  view.  Priestley  had  ob- 
served that  plants  possess  the  faculty  of  purifying  air 
that  had  been  vitiated  by  the  breathing  of  animals  or 
by  combustion,  and  it  had  been  discovered  that  the 
bubbles  of  gas  which  growing  plants  emit  when 
plunged  under  water  consist  chiefly  of  oxygen. 

Ingenhousz  had  shown  that  these  phenomena 
demand  the  presence  of  sunlight,  and  Sennebier  that 
the  oxygen  emitted  by  plants  finds  its  source  in  the 
carbon  dioxide  absorbed  from  the  air.  De  Saussure, 
who  worked  at  the  end  of  the  last  century,  had,  by 
experiments  that  were  approximately  quantitative, 
shown  that  in  sunlight  plants  increase  the  quantity  of 


88  JUSTUS   VON   LIEBIG: 

carbon,  hydrogen,  and  oxygen  in  their  tissues,  and 
that  this  is  done  at  the  expense  of  carbon  dioxide  and 
water  ;  by  an  important  experiment  he  had  also  proved 
that  the  increase  of  carbon  and  of  the  components  of 
water  correspond  pretty  closely  to  what  we  know  to 
be  the  proportions  of  them  in  the  carbohydrates. 
(See  p.  85.)  He  had  also  recognised  the  usefulness  of 
minerals,  that  they  must  come  from  the  soil,  and  had 
called  attention  to  the  probability  that  the  origin  of 
the  mineral  constituents  of  the  animals  was  to  be 
found  in  these  incombustible  substances  extracted  by 
plants  from  the  earth.  In  regard  to  the  already  much 
debated  point  of  the  origin  of  the  nitrogen  of  plants, 
De  Saussure  was  of  opinion  that  nitrogen  was  rather 
given  to  the  air  than  taken  from  it,  and  that  the 
sources  of  nitrogen  were  probably  the  nitrogenous 
substances  in  the  soil  and  the  ammonia  of  the  air, 
which  is  largely  brought  down  to  the  earth  by  rain. 
On  the  whole,  though  he  does  not  seem  to  have 
distinctly  disowned  the  humus  theory  (see  below),  he 
regarded  the  air  as  the  main  source  of  the  carbon, 
hydrogen,  and  oxygen  of  plants,  and  the  earth  as 
valuable  in  affording  supplies  of  mineral  matter  and 
nitrogenous  substances. 

The  humus  theory. — Owing  to  the  fact  that 
virgin  soils  are  often  particularly  well  suited  for  the 
cultivation  of  plants,  and  that  these  virgin  soils  have 
been  found  to  be  very  rich  in  vegetable  mould,  or 
humus,  it  had  come  to  be  supposed,  prior  to  the 
date  of  Liebig's  earliest  writings  on  agricultural 
chemistry,  by  many  chemists  and  agriculturists,  that 
this  vegetable  mould  was  the  source  of  the  fertility 
of  these  soils.  By  an  extension  of  this  idea  many 
vegetable  physiologists  ascribed  the  fertility  of  all 


HIS    LIFE    AND   WORK.  89 

soils  to  its  presence,  and  even  regarded  it  as  the 
chief  nutriment  of  the  plants ;  it  was  supposed  by 
them  that  the  humus  was  extracted  from  the  soil 
by  the  roots  of  the  growing  plants. 

In  Germany  this  view  Avas  very  widely  accepted. 
Even  De  Saussure  is  said  by  Ernst  von  Meyer,  in  his 
history  of  chemistry,  not  to  have  kept  himself  quite 
clear  of  this  error,  though  he  realised  much  better 
than  many  others  that  the  air,  more  than  the  earth,  was 
the  source  of  the  carbon  and  hydrogen  of  plants.  In 
England,  as  Dr.  Playfair  pointed  out  long  ago,  this 
idea  of  the  function  of  humus  was  by  no  means  so 
unreservedly  accepted  when  Liebig  wrote;  but  one 
rises  from  a  careful  examination  of  what  Davy, 
Daubeny,  Thomson,  and  Brande  wrote  during  the  early 
part  of  the  century,  very  far  from  convinced  that 
these  authorities  unreservedly  accepted  the  alternative 
hypothesis  suggested  by  Priestley's  observations  on 
the  purifying  of  the  air  by  plants.  In  fact,  even  in 
England,  a  clear  perception  of  the  source  of  the  carbon 
of  plants  was  still  to  seek.  Thus  Brande,  writing  as 
late  as  1836,  still  doubted  whether  plants  could 
efficiently  remove  the  carbonic  acid  gas  from  the  air, 
and  considered  that  the  carbon  of  manure,  reduced  by 
putrefaction  to  a  soluble  state,  was  an  important  source 
of  supply. 

Liebig,  in  dealing  with  this  subject,  went  straight 
to  the  root  of  the  matter.  Humus  is  of  very  vari- 
able composition,  and  is  only  soluble  in  water  when 
freshly  precipitated ;  it  becomes  quite  insoluble  after 
drying,  and  after  it  has  been  exposed  to  a  freezing 
temperature.  Both  the  heat  of  summer  and  the  cold 
of  winter,  therefore,  render  this  substance  insoluble. 
This  is  confirmed  by  the  fact  that  water  does  not 


90  JUSTUS   VON   LIEBIG: 

dissolve  anything  more  than  a  mere  trace  of  organic 
matter  from  good  garden  soil,  and  that  the  decayed 
wood  of  various  trees,  which  largely  consists  of  humus- 
like  matter,  is  also  practically  insoluble. 

But,  in  order  that  humus  shall  be  absorbed  by 
plants,  it  must  first  become  capable  of  entering  into 
solution.  It  follows,  that  humus,  as  it  occurs  in  the 
earth,  cannot  serve  to  nourish  plants. 

This  was  not  denied  by  physiologists.  And  in 
order  to  overcome  the  difficulty,  they  assumed  that 
the  lime  and  the  alkalis  found  in  the  ashes  of  vege- 
tables render  the  humus  soluble,  and  so  fit  it  for 
being  assimilated  by  the  roots  of  plants. 

It  is  true  that  alkalis  and  alkaline  earths  (e.g.  lime) 
do  exist  in  different  soils  in  sufficient  quantities  to 
form  compounds  with  humus,  and  that  humus  is 
rendered  soluble  in  water  by  their  presence.  One 
kilogramme  of  lime,  for  example,  will  combine  with 
10*9  kilos,  of  humic  acid. 

To  test  the  validity  of  the  hypothesis  based  upon 
these  facts,  Liebig  made  various  calculations,  the 
results  of  which  clearly  showed  that  the  amount  of 
humus  which  could  possibly  be  obtained  by  the  plants 
on  a  given  area  is  far  too  small  to  account  for  the 
vegetables  actually  produced,  even  after  making  all 
sorts  of  impossible  assumptions  in  favour  of  the  theory 

He  supported  the  facts  brought  to  light  by  his 
calculations  by  others. 

Thus,  he  showed  that  the  proportion  of  carbon 
produced  on  one  acre  of  cultivated  land  from  such 
various  crops  as  fir-wood,  pine-wood,  beech-wood, 
beet-root,  rye  and  hay,  is  remarkably  constant  under 
dissimilar  conditions  of  cultivation. 

Also,  that  carbon  may  be  removed  to  some  extent 


HIS    LIFE   AND    WORK.  91 

from  a  forest  or  meadow  in  the  form  of  wood  or 
hay,  and  that,  in  spite  of  this,  the  soil  will  become 
richer,  not  poorer,  in  carbon.  And  finally,  he  clinched 
the  argument  by  pointing  out  that  since  it  is  uni- 
versally admitted  that  humus  is  only  produced  by 
the  decay  of  plants,  no  primitive  humus  can  have 
existed  for  the  first  plants,  for  plants  must  have  pre- 
ceded the  humus. 

These  were  the  facts  and  arguments  by  which, 
once  and  for  all,  Liebig  rendered  the  humus  theory 
utterly  untenable  by  any  reasonable  human  being. 

Anarchy,  however,  is  no  more  acceptable  in 
science  than  in  society,  and  Liebig  was  the  last  man 
to  be  satisfied  with  the  mere  overthrow  of  an 
erroneous  theory.  He  was  bound  by  his  nature  to 
ask  himself  the  question — Whence,  then,  did  the  first 
vegetables  obtain  their  carbon  ? 

Having  thus  demolished  the  humus  theory,  Liebig 
proceeded  to  investigate  its  rival.  Ever  since 
Priestley's  observations,  in  1771,  on  the  influence  of 
plants  on  the  air,  vegetable  physiologists  had,  more 
especially  in  England,  shown  an  inclination  to 
suppose  that  part  at  least  of  the  carbon  of  plants 
is  derived  from  the  carbonic  acid  gas  of  the  air, 
and  as  early  as  1807  Thomson  had  observed  that  if 
plants  are  deprived  of  this  gas  they  droop  their 
leaves,  which  then  refuse  to  fulfil  their  functions. 
De  Saussure  and  others  had  abundantly  confirmed  the 
English  observer's  conclusions,  and  it  was  beginning 
to  be  generally  admitted  in  this  country  that  prob- 
ably a  large  quantity  of  carbon  is  obtained  by  plants 
from  this  source,  and  that  oxygen  is  simultaneously 
supplied  to  the  air.  But  further  progress  was  retarded, 
partly  by  the  apparent  existence  of  an  alternative 


92  JUSTUS   VON   LIEBIG: 

source  of  supply  in  the  humus  of  the  soil,  and  partly 
by  the  discovery  by  Ingenhousz  that,  although  in 
sunlight  plants  absorb  carbonic  acid  gas  and  give 
out  oxygen,  in  the  dark,  on  the  contrary,  they  rather 
injure  the  air  than  improve  it,  as  they  then  absorb 
oxygen,  and  in  some  cases  emit  carbonic  acid  gas. 
The  oxygen  given  out  in  the  light  was,  moreover, 
even  said  to  correspond  to  that  absorbed  in  the  dark. 
Naturally,  under  these  circumstances  it  seemed 
doubtful  whether,  on  the  whole,  very  much  carbon 
was  really  derived  from  the  air  by  plants,  and  the 
uncertainty  on  this  point  helped  to  maintain  the 
position  of  the  humus  theory  until,  as  we  have 
seen,  Liebig  demolished  it  in  1840.  But  one  of  the 
most  remarkable  facts  about  the  composition  of  the 
air  is  this,  that  in  spite  of  the  vast  consumption  of 
oxygen  by  animals,  by  combustion,  and  in  decay, 
the  proportion  of  oxygen  in  pure  air  is,  at  all  times 
and  in  all  climates,  practically  uniform.  The  analysis 
of  air  always  shows  that  one  hundred  volumes  of  air 
contain  twenty-one  volumes  of  oxygen.  And  yet,  vast 
as  is  the  store  of  oxygen  in  the  air,  so  great  is  the  con- 
sumption thereof  that  the  supply  cannot  be  considered 
to  be  inexhaustible.  Liebig,  indeed,  made  a  calculation 
Avhich  showed  that  at  the  rate  at  which  we  now  use  it 
the  air  would  become  quite  unfit  for  us  in  less  than 
300,000  years,  owing  to  loss  of  oxygen  alone,  if  the 
supply  were  not  renewed.  How  is  it  possible,  he 
asked,  that  with  so  vast  a  consumption  of  oxygen  the 
supply  should  remain  so  nearly  constant;  that  the 
analysis  of  air  taken  from  jars  buried  in  Pompeii 
nearly  2,000  years  ago  should,  under  these  circum- 
stances, present  so  nearly  the  same  composition  as  a 
sample  taken  from  the  air — it  may  be  yesterday. 


HIS    LIFE    AND    WORK.  93 

Again,  it  had  been  found  in  Liebig's  day,  from  the 
analyses  of  De  Saussure,  that  the  proportion  of  car- 
bonic acid  gas  in  the  air  was  actually  not  above  one 
part  in  a  thousand.*  What  then  has  become  of  the 
vast  quantities  of  carbonic  acid  gas  that  have  been 
poured  into  the  air  during  countless  .ages  by  the 
breathing  of  animals,  by  the  process  of  combustion, 
and  in  the  decay  of  organic  substances — quantities  so 
great  that,  according  to  the  above-mentioned  calcula- 
tion, in  a  period  of  100,000  years  they  must  have 
caused  an  accumulation  of  this  gas  amounting  to 
several  parts  by  volume  in  every  one  hundred  volumes 
of  air  ? 

We  have  even  reason  to  believe  that  the  propor- 
tion of  carbonic  acid  may  once  have  been  greater  than 
now,  and  yet,  in  spite  of  the  enormous  volumes  of 
this  gas  which  are  daily  poured  into  the  air,  there  is 
to-day  only  a  trace  of  it  present.  It  is  evident,  said 
Liebig,  that  the  invariable  proportions  of  carbonic 
acid  gas  and  oxygen  in  the  atmosphere  and  the  mere 
trace  of  the  former  that  is  found  there,  in  spite  of  the 
enormous  and  never-ending  supplies,  must  be  the 
result  of  some  cause  which  prevents  the  increase  of 
carbonic  acid  gas  by  removing  that  which  is  con- 
stantly forming ;  and  that  there  must  be  some  means 
of  replacing  the  oxygen  removed  from  the  air  by  the 
processes  of  combustion  and  putrefaction,  as  well  as  by 
the  respiration  of  animals. 

He  found  the  answer  to  these  questions  in  the 
data  supplied  by  his  predecessors,  Priestley,  Sennebier, 
and  De  Saussure.  Both  these  causes  are  united  in  the 
processes  of  vegetable  life. 

*  The  more  refined  methods  of  modern  analysis  place  the  propor- 
tion still  lower. 


94  JUSTUS   VON   LIEBIG: 

The  carbon  of  plants  cannot  come  from  the  earth ; 
it  must  be  derived  from  the  atmosphere.  The  only 
form  of  carbon  which  exists  in  the  atmosphere  is 
carbonic  acid  gas,  or  oxide  of  carbon ;  it  follows  that 
this  must  be  the  source  of  the  carbon  of  vegetables. 

But,  further,  the  analysis  of  plants  shows  that  the 
greater  part  of  their  constituents  are  composed  of 
carbon,  together  with  hydrogen  and  oxygen,  in  the 
proportions  in  which  they  form  water ;  from  this  it 
follows  that  the  oxygen  required  for  the  nutrition  of 
a  plant  can  be  mainly  supplied  by  the  water  which  it 
assimilates,  since  hydrogen  enters  into  the  food  of 
plants  almost  entirely  in  this  form,  and  if  this  be  so 
the  oxygen  of  the  carbonic  acid  gas  is  quite  unneces- 
sary for  plants,  and  must  escape  into  the  air  in  the 
gaseous  form.  As  carbonic  acid  gas  contains  its  own 
volume  of  oxygen,  the  atmosphere  must  thus  receive 
for  every  volume  of  carbonic  acid  gas  decomposed  by 
the  plants  an  equal  volume  of  oxygen. 

This  view  was  not  only  in  accordance  with  the 
facts  already  mentioned,  but  De  Saussure  had  shown 
that  the  gain  in  weight  of  a  growing  plant  is  greater 
than  can  be  accounted  for  by  the  carbon  assimilated, 
which  agrees  with  the  supposition  that  the  elements  of 
water  are  assimilated  at  the  same  time  as  the  carbon. 

"  The  life  of  plants,"  said  Liebig,  "  is  closely  con- 
nected with  that  of  animals,  in  a  most  simple  manner, 
and  for  a  wise  and  sublime  purpose. 

"  The  presence  of  a  rich  and  luxuriant  vegetation 
may  be  conceived  without  the  concurrence  of  animal 
life,  but  the  existence  of  animals  is  undoubtedly  de- 
pendent upon  the  life  and  development  of  plants. 

"  Plants  not  only  afford  the  means  of  nutrition  for 
the  growth  and  continuance  of  animal  organisation, 


HIS    LIFE    AND    WORK.  95 

but  they  likewise  furnish  that  which  is  essential  for 
the  support  of  the  important  vital  process  of  respira- 
tion ;  for,  besides  separating  all  noxious  matters  from 
the  atmosphere,  they  afford  an  inexhaustible  supply 
of  pure  oxygen,  and  they  thus  make  up  to  the  air  the 
loss  constantly  sustained  by  it.  Animals,  on  the 
other  hand,  expire  carbonic  acid  gas,  whilst  plants 
inspire  it,  and  thus  the  composition  of  the  atmosphere, 
the  medium  in  which  both  live,  is  maintained  con- 
stantly unchanged." 

It  was  only  necessary  to  prove  that  the  amount  of 
carbonic  acid  gas  in  the  air,  at  most  only  one- tenth 
per  cent.,  is  sufficient  to  supply  the  wants  of  the 
whole  vegetation  on  the  surface  of  the  earth,  in  order 
to  finally  establish  the  doctrine  so  clearly  enunciated 
in  the  above  paragraphs.  This  was  not  difficult,  for 
the  total  mass  of  carbon  in  the  air  is  immense, 
although  its  proportion  is  small  relatively  to  that 
of  the  other  constituents.  But  is  it  possible  that  it 
can  be  absorbed  sufficiently  rapidly  from  so  dilute  a 
mixture  ? 

This  seemed  to  Liebig  quite  likely  to  be  the  case 
when  he  considered  the  wide  area  which  the  leaves 
offer  to  the  gas,  and  the  rapidity  with  which  a  lime- 
wash,  spread  on  a  wall,  will  absorb  this  gas.  One 
square  decimetre  of  such  a  surface,  in  the  course  of 
six  washings,  has  been  known  to  absorb  in  four  days 
as  much  carbonic  acid  gas  as  will  produce  three- 
quarters  of  a  gram  of  calcium  carbonate.  This 
quantity  was  found  by  Liebig  to  be  several  times  as 
great  as  that  which  is  assimilated  by  the  leaves  and 
roots  of  plants  growing  on  an  equal  area,  in  an  equal 
space  of  time.  It,  therefore,  seemed  not  unreasonable 
to  answer  the  above  question  in  the  affirmative. 


96  JUSTUS   VON   LIEBIG: 

The  evolution  of  carbon  dioxide,  which  occurs  at 
night,  seemed  to  Liebig  to  be  a  natural  but  secondary 
incident.  Since  plants  were  supposed  to  absorb  car- 
bon dioxide  during  the  day,  but  only  to  assimilate  its 
carbon  in  sunlight,  he  thought  it  likely  that  at 
night  some  of  the  undecomposed  gas  would  be  re- 
turned to  the  air,  together  with  water  vapour  ;  and  he 
considered  that  the  nocturnal  absorption  of  oxygen, 
observed  by  Ingenhousz,  was  due  to  changes  not  at  all 
connected  with  the  life  of  the  plant,  caused  by  the 
action  of  the  oxygen  of  the  air  on  the  organic  sub- 
stances composing  its  leaves,  flowers,  and  fruit.  In 
this  Liebig  was  doubtless  wrong.  The  evolution  of 
of  carbon  dioxide  and  absorption  of  oxygen  by  plants 
at  night  are  now  recognised  as  the  characteristic  ac- 
companiments of  the  processes  of  cell-division  and 
cell-multiplication,  by  which  their  structure  is  in- 
creased, and  which  take  place,  at  any  rate,  chiefly 
during  night. 

But  on  the  main  point  he  was  right,  for  it  is  now 
fully  recognised  that  the  oxygen  absorbed  and  the 
carbon  dioxide  set  free  at  night,  which  misled  so 
many  botanists  and  vegetable  physiologists,  are  far 
from  being  sufficient  to  counterbalance  the  carbon 
dioxide  taken  up,  and  the  oxygen  simultaneously  set 
free  during  the  hours  of  daylight,  on  which  all  plant 
life  is  founded.* 

One  of  the  reasons  which  had  led  physiologists  to 
imagine  that  humus  was  particularly  well  suited  for 

*  Davy  showed  the  producing  of  oxygen  from  carbon  dioxide  by 
plants  very  elegantly,  hy  growing  grass  under  glass  receivers  standing 
in  water,  and  containing  air  supplied  with  small  additional  quantities 
of  carbonic  acid  gas  from  time  to  time.  After  the  lapse  of  eight  days, 
the  air  in  the  receiver  was  found  to  be  very  decidedly  enriched  with 
oxygen. 


HIS    LIFE    AND   WORK.  97 

nourishing  plants  was  the  fact  that  it  differs  from 
wood  chiefly  in  containing  an  excess  of  carbon.  Like 
wood,  it  contains  carbon,  together  with  hydrogen  and 
oxygen,  in  the  proportions  in  which  they  combine  to 
form  water,  but,  relatively  to  the  proportion  of  carbon, 
the  proportion  of  water  is  less.  Misled  by  this  fact, 
the  physiologists  concluded  that  this  similarity  of 
composition  between  humus  and  the  constituents  of 
plants  must  favour  the  assimilating  of  the  former  by 
plants.  Humus  had  only  to  unite  with  water  in  order 
to  form  woody  tibre. 

In  this,  as  Liebig  pointed  out,  they  went  wrong,  in 
consequence  of  trusting  that  most  dangerous  guide — 
an  argument  from  analogy.  They  had  no  right  to  as- 
sume that  the  vital  processes  of  plants  are  in  this  sense 
similar  to  those  of  animals.  The  vital  process  of  a 
plant  depends,  as  Liebig  has  taught  us,  on  a  change  by 
which  it  recovers  carbon  from  a  simple  inorganic  sub- 
stance. Plants,  unlike  animals,  are  not  fitted  to  assimi- 
late the  products  of  plant  life.  On  the  contrary — as  was, 
indeed,  already  known — when  sugar,  gum,  or  starch  are 
absorbed  by  a  plant,  these  compounds  do  not  nourish 
it,  for  the  very  life  of  a  plant  consists  in  the  elabora- 
ting of  these  substances.  Humus,  therefore,  and  the 
other  products  of  life,  can  by  no  means  be  assumed 
to  be  fit  for  the  support  of  plant  life. 

Here  Liebig  drew  a  clear  and  broad  distinction 
between  the  vital  functions  of  plants  and  animals, 
\vhich  was  the  corner-stone  of  his  work  in  vegetable 
and  animal  chemistry. 

But,  although  humus  is  not  the  food  of  plants, 

Liebig  does  not  teach  us  to  see  in  it  mere  dead,  useless 

matter.     When  a  leaf,  a  twig,  or  a  tree  falls,  it  enters 

on  a  new  series  of  changes,  in  the  course  of  which  it 

G 


98  JUSTUS  VON  LIEBIG: 

will  ultimately  pass  once  more  into  the  condition  of 
the  simple  oxidised  compounds,  which  can  afford 
nutriment  for  a  new  generation  of  plants.  Humus 
represents  one  of  the  stages  of  this  series  of  transfor- 
mations. It  is  woody  fibre  in  a  state  of  decay.  In 
contact  with  air,  as  in  well-tilled  ground,  it  undergoes 
steady  if  slow  oxidation,  and  thus  it  becomes,  according 
to  Liebig,  the  source  of  carbonic  acid  gas  for  very  young 
plants,  the  seedlings,  to  which  it  offers  a  supply  of 
this  necessary  substance  before  the  development  of 
their  roots  and  leaves  enables  them  to  take  the  latter 
from  the  air. 

And,  besides  this,  the  carbonic  acid  gas,  by  entering 
into  solution  in  the  water  which  falls  as  rain,  renders 
this  more  capable  of  disintegrating  minerals,  and  thus 
promotes  the  processes  by  which  the  saline  constitu- 
ents of  rocks  become  available  for  plants,  Finally, 
the  oxidation  of  the  humus  ultimately  liberates  the 
saline  material  of  dead  plants,  so  that  they  become 
once  more  fit  to  serve  for  the  sustenance  of  their 
successors. 

Humus,  then,  represents  mainly  certain  stages  in 
the  primitive  processes  which  connect  one  genera- 
tion of  vegetables  with  those  which  succeed  it,  so  far 
as  concerns  those  parts  of  vegetables  which  are  not 
utilised  by  man. 

These  conceptions  concerning  the  relations  of 
plants  and  animals  to  one  another,  and  to  the  air 
they  live  in,  which  we  thus  owe  to  Liebig,  have  now  so 
completely  taken  their  stand  among  the  common- 
places of  science,  that  most  likely  hardly  any  of  the 
readers  of  this  little  book  were  unfamiliar  with  them 
when  they  opened  its  pages ;  and  yet,  probably,  very 
many,  if  not  most,  were  unaware  how  recently  they 


HIS    LIFE   AND   WORK.  99 

have  become  part  of  the  equipment  of  mankind,  by 
what  steps  they  have  been  reached,  or  who  it  was 
that  first  traced  out  the  few  simple  laws  which 
underlie  the  relations  of  the  two  kingdoms  of  organic 
nature,  by  disentangling  the  intricacies  of  problems, 
which,  simple  as  Liebig  has  made  them  seem  to  us, 
once  appeared  to  be  almost  beyond  solution. 

Even  in  1840,  however,  the  most  advanced  chem- 
ists and  biologists  were  by  no  means  unprepared 
for  such  developments  as  those  which  we  have  just 
considered,  for,  as  we  have  seen,  the  work  of  several 
then  living  investigators  had  already  largely  paved 
the  way  for  them.  Indeed,  only  about  a  year  later 
Dumas,  on  behalf  of  himself  and  of  Boussingault, 
delivered  a  lecture  at  the  conclusion  of  his  course  of 
chemistry  in  the  Medical  School  of  Paris,  entitled 
" Essai  de  Statiqiw  Chimique  des  Stres  Organises"  in 
which  they  presented  a  resume  of  their  chemical  and 
physiological  researches,  and  propounded  ideas  closely 
corresponding  with  those  previously  expressed  by 
Liebig,  and  in  which  an  even  broader  view  of  the 
relations  of  the  vegetable  and  animal  worlds  was 
brought  forward  and  sustained.  And  before  this,  half 
a  century  earlier,  Lavoisier,  the  father  of  modern 
chemistry,  had  anticipated  the  ideas  which  Liebig 
was,  as  we  have  seen,  the  first  to  establish  beyond  the 
possibility  of  further  doubt. 

"  Plants,"  wrote  Lavoisier  in  a  document  only  dis- 
covered after  the  publication  of  the  first  three  volumes 
of  his  collected  works  in  1862,  "  plants  derive  the 
materials  necessary  for  their  formation  from  the  air 
Avhich  surrounds  them,  from  the  water,  and  in  general 
from  the  mineral  kingdom." 

"  Animals  feed  on  plants,  or  other  animals  fed  by 


100  JUSTUS   VON   LIEBIG  : 

plants,  so  that  the  substances  composing  them  are,  in 
the  last  instance,  always  drawn  from  air  and  from  the 
mineral  kingdom." 

"On  the  other  hand,  fermentation,  putrefaction, 
and  combustion  continually  restore  to  the  air  and  the 
mineral  kingdom  the  principles  borrowed  from  them 
by  plants  and  animals." 

But  whilst  the  discovery  of  this  document  must 
add  to  our  admiration  for  the  immortal  Lavoisier, 
and  sharpens,  if  that  is  possible,  our  regret  for  his 
untimely  end,  it  rather  adds  to,  than  detracts  from, 
the  honour  due  to  his  illustrious  successor  that  he 
should  have  originated  independently,  and  in  so 
nearly  the  same  form,  the  brilliant  speculations  of  his 
great  fore-runner ;  and  especially  is  this  the  case  when 
we  remember  that,  aided  by  the  advance  of  knowledge, 
he  succeeded  in  establishing  the  truth  of  these  specu- 
lations and  in  building  upon  them  one  of  the  pillars 
of  the  natural  sciences. 

Plants  do  not  consist  of  carbon  only  ;  they  contain 
also,  besides  the  elements  of  water,  sulphur,  nitrogen, 
phosphorus,  and  mineral  matter.  With  regard  to  the 
sources  of  the  hydrogen,  the  oxygen,  and  the  sulphur 
of  plants,  Liebig  considered  that  the  first-named 
element,  at  any  rate  so  far  as  that  part  of  it  which  is 
in  the  non-nitrogenous  compounds  is  concerned,  is 
derived  from  water ;  that  the  oxygen  is  provided 
either  by  the  water  or  by  the  carbonic  acid  gas ;  and 
that  the  sulphur  has  its  origin  in  the  sulphates  which 
are  present  in  sufficient  quantities  in  soils. 

Besides  the  chief  elements  mentioned  above,  there 
is  another — viz.  nitrogen — which  exists  in  every  part 
of  every  plant,  and  which  cannot  be  supposed  to  be 
of  less  importance,  although  it  is  present  in  very 


HIS    LIFE    AND   WORK.  101 

much  smaller  quantities.  The  question  in  what  form 
does  nature  supply  this  nitrogen  has  for  many  years 
been  the  subject  of  almost  constant  research  and 
discussion. 

Nitrogen  is,  of  all  the  elements,  one  of  the  least 
apt  to  enter  into  direct  combination,  and  hence  it 
has  appeared  improbable  to  chemists  that  the  free 
nitrogen  of  the  air  could  be  the  source  from  which 
plants  gain  their  supply  of  it. 

Liebig  at  first  was  of  opinion  that  the  source  of 
the  nitrogen  of  plants  lay  in  the  ammonia  produced 
by  the  putrefaction  of  plants  and  animals,  the  remains 
of  one  generation  producing  by  decay  what  was  re- 
quired for  another.  A  good  deal  of  nitrogen  is  thus 
returned  to  the  soil  in  the  form  of  ammonia  in 
manure ;  some  is  yielded  by  the  refuse  of  the  crops, 
but  on  a  given  farm,  unless  all  the  products  are  con- 
sumed at  home,  there  must  be  a  loss  in  consequence 
of  the  selling  of  certain  products.  In  any  event  some 
ammonia  must  also  be  lost  during  the  process  of  decay 
(we  have  all  of  us  recognised  the  odour  of  smelling  salts 
in  a  badly-ventilated  stable  at  one  time  or  another)  ; 
hence,  practically,  the  nitrogen  returned  to  the  soil 
of  a  given  farm  by  an  agriculturist  must  always 
be  less  than  was  contained  in  the  crops  grown. 
Liebig  therefore  concluded  that  the  ammonia  brought 
down  by  the  rain  probably  constitutes  a  very  im- 
portant source  of  supply.  This  opinion  was  soon 
challenged  by  Boussingault,  who  laid  much  more 
weight  on  the  importance  of  manures  as  a  source  of 
nitrogen,  and  considered  the  supply  obtained  from 
the  air  to  be  of  less  importance. 

In  1843,  in  a  new  edition  of  his  book,  Liebig  may 
be  said  to  have  laid  the  foundation  of  the  celebrated 


102  JUSTUS   VON    LIEBIG: 

"  mineral  theory  "  of  agriculture.  He  also  returned  to 
the  subject  of  nitrogen,  and  in  his  developed  treatment 
of  it  he  pointed  out  that  whilst  nitrogen  can  only  be 
made  to  enter  into  combination  with  the  other  con- 
stituents of  plants  by  the  most  powerful  chemical 
means,  and  whilst  this  element  is,  moreover,  frequently 
emitted  by  plants,  ammonia,  on  the  other  hand,  is 
remarkable,  like  water,  for  the  number  of  the  trans- 
formations which  it  undergoes,  and  for  the  various  and 
opposite  characters  of  the  substances  which  it  produces. 
As  carbonic  acid  gas  is  the  last  product  of  decay  so  far 
as  carbon  is  concerned,  so  is  ammonia  the  form  in 
which  the  nitrogen  of  animal  bodies  is  returned  to 
the  air  during  putrefactive  processes.  The  bodies  of 
a  thousand  million  men  and  of  thousands  of  millions 
of  animals  are  renewed  every  thirty  years,  and  by 
their  decay  their  nitrogen  is  converted  into  ammonia 
which  escapes  into  the  air,  to  be  dissolved,  for  it  is 
eminently  soluble,  by  water  in  the  form  of  rain,  and 
so  be  carried  back  to  the  roots  of  plants,  except  in 
regard  to  that  part  of  it  which  is  washed  more  directly 
into  the  earth  during  decay,  or  is  introduced  fixed 
in  the  form  of  manure  by  the  cultivator  of  the  soil. 

Although  Liebig  by  no  means  denied  that  nitrogen 
may  be  supplied,  with  advantage,  in  the  form  of  manure, 
he  was  led  by  the  evidence  then  available  to  conclude 
that  the  ammonia  in  the  air,  like  the  carbonic  acid 
gas,  is  by  itself  sufficient  to  supply  nitrogen  to  many 
crops.  This  opinion  was  vehemently  contested  by  his 
opponents ;  and  partly  because  the  data  available 
were  incorrect,  and  partly  in  consequence  of  mis- 
conceptions, it  became  the  subject  of  a  warm  and  pro- 
longed discussion.  Important  as  this  discussion  was 
to  agriculturists,  its  details  >vould  not  be  interesting  to 


HIS    LIFE    AND    WORK.  103 

general  readers ;  but  it  may  be  mentioned  that  this 
memorable  dispute  was  only  settled  after  Liebig's 
death  by  the  important  discovery,  made  not  very  long 
since  by  Professor  Hellriegel  and  Dr.  Wilfarth,  that 
the  power  of  the  leguminous  plants  to  assimilate  free 
nitrogen*  is  dependent  upon  the  presence  of  certain 
minute  organisms  which  flourish  in  and  around  their 
roots,  where  they  cause  the  production  of  tuber-like 
formations  which  swarm  with  the  micro-organisms 
and  abound  in  nitrogen. 

But  plants  do  not  consist  only  of  organic  sub- 
stances, and  one  of  the  numerous  questions  which 
puzzled  the  early  workers  in  agricultural  chemistry 
was  the  origin  and  function  of  the  mineral  parts  of 
plants.  The  later  upholders  of  the  humus  theory, 
though  the}7  could  not  absolutely  deny  the  import- 
ance of  mineral  matters  to  plants,  held  that  they 
were  not  exactly  essential  to  their  growth,  but  rather 
mere  stimulants — useful  perhaps — but  still  stimulants, 
and  not  a  necessary  part  of  their  food.  Some 
of  them,  indeed,  held  that  the  minerals  were  pro- 
duced in  the  plants  by  their  vital  forces ;  and,  astonish- 
ing as  it  may  seem,  in  1800  the  Berlin  Academy 
awarded  a  prize  to  an  apothecary,  one  Schneder,  for 
an  essay  in  which  he  claimed  that  he  had  proved 
by  actual  experiment  that  plants  produce  mineral 
matter  by  their  vital  forces,  and,  although  this  paper 
was  justly  criticised  by  De  Saussure,  Schneder's 
views,  as  late  as  1807,  received  a  distinct  measure  of 
support  from  the  English  chemist,  Dr.  Thomson,  who 
wrote  that  Saussure's  remarks  are  "  by  no  means 
sufficient  to  set  aside  the  experiments  of  Schraeder." 
Sir  Humphry  Davy,  however,  would  by  no  means 

*  Established  in  recent  years  by  Messrs.  Lawes  and  Gilbert. 


104  JUSTUS   VON   LIEBIG  : 

accept  his  results,  and  indeed  detected  the  source  of 
the  error  made  by  those  inquirers  who  "  adopted  that 
sublime  generalisation  of  the  ancients  that  matter  is 
the  same  in  essence,  and  that  different  substances,  con- 
sidered as  elements  by  chemists,  are  merely  different 
arrangements  of  the  same  indestructible  particles." 

But  Liebig  first  seems  to  have  fully  understood  the 
importance  of  the  mineral  foods  of  plants,  of  which  he 
gives  us  many  illustrations,  from  which  the  following 
examples  are  taken. 

Years  ago  it  was  the  custom,  in  some  parts  of 
Germany,  to  permit  the  poor  people  to  remove  the 
leaves  and  twigs  of  trees  from  the  forests,  for  use  as 
litter  for  their  cattle.  It  was  found,  however,  that 
the  trees  suffered  very  much,  far  more,  for  example, 
than  from  the  removal  of  an  equal  mass  of  wood 
alone.  Why  was  this  ?  The  analysis  of  the  ashes  of 
twigs  and  leaves  and  of  wood  gives  us  the  reason.  The 
ash  of  the  former  contains  much  more  alkali  than 
that  of  the  latter ;  evidently  the  removal  of  the  twigs 
and  leaves,  by  withdrawing  alkali,  robbed  the  trees 
of  a  part  of  their  food — starved  them,  in  fact.  Had  the 
leaves  been  allowed  to  remain,  they  would  presently, 
by  their  decay,  have  restored  their  alkaline  matter  to 
the  soil  ready  for  further  use.* 

The  tobacco  plant  and  the  vine  give  ashes  which 
contain  much  lime.  They  do  not  grow  well  on  soils 
devoid  of  lime;  but  when  lime  is  added  to  such 
soils,  the  enriched  soils  become  more  fit  for  the  growth 
of  tobacco  and  grapes.  We  cannot  avoid  the  inference 
that  lime  forms  an  essential  part  of  the  food  of  the 
tobacco  plant  and  of  the  vine. 

*  It  must  not  be  supposed  that  this  is  the  sole  cause  of  the  injury 
done. 


HIS    LIFE    AND    WORK.  105 

Again,  at  Bingen-on-the-Khine,  the  produce  of  the 
vines  was  at  one  time  greatly  increased  by  the  use  of 
nitrogenous  manures,  but,  after  a  while,  these  were 
found  to  lose  their  effect,  and  the  condition  of  the 
plants  fell  off  so  seriously  that  their  possessor  had 
great  reason  to  regret  the  experiment.  By  the 
manure  employed,  as  Liebig  explained,  the  vines 
were  hastened  in  their  growth,  so  that  in  a  few 
years  they  exhausted  the  soil  of  certain  minerals,  and 
these  being  absent  from  the  manures  employed,  the 
plants  were  afterwards  starved.  Other  vines  on  the 
Rhine,  when  treated  with  manures  rich  in  potash  and 
poor  in  nitrogen  have  lived  for  as  much  as  a  hundred 
years. 

By  such  facts  as  these,  Liebig  made  it  clear  that  the 
mineral  matter  of  the  soil  is  as  essential  to  the  well- 
being  of  plants  as  carbonic  acid  gas,  water  and 
ammonia. 

"  Plants,"  he  says,  "  live  upon  carbonic  acid  gas, 
ammonia,  water,  phosphoric  acid,  sulphuric  acid, 
silicic  acid,  lime,  magnesia,  potash,  and  iron ;  many 
of  them  also  require  common  salt.  .  .  ." 

"  Manure,  the  excrements  of  the  lower  animals  and 
man,  does  not  act  on  plant  life  through  the  direct 
assimilation  of  its  organic  elements,  but  indirectly 
through  the  products  of  its  decomposition  and  putre- 
faction. That  is,  by  the  transforming  of  its  carbon 
into  carbonic  acid  gas,  and  of  its  nitrogen  into  am- 
monia or  nitric  acid,  Organic  manure,  which  consists 
of  portions  or  debris  of  plants  and  animals,  may  be 
replaced  by  the  inorganic  compounds  into  which  it 
breaks  up  in  the  ground." 

From  what  has  been  said  it  follows,  as  Liebig 
pointed  out,  that  we  must  replenish  the  soil  by  adding 


106  JUSTUS   VON    LIEBIG  : 

whatever  minerals  have  been  withdrawn  from  it  by 
our  crops  if  we  desire  to  avoid  exhausting  it. 

Since  the  supplies  of  carbon  dioxide,  of  water, 
and  of  ammonia  are,  for  the  most  part,  beyond 
our  control,  and  since,  moreover,  these  are  ample,  it 
appeared  to  him  evident  that  the  chief  work  of  the 
agriculturist,  after  keeping  his  soil  in  proper  con- 
dition by  tilling  it,  is  to  prevent  loss  of  mineral 
matter,  or  when  that  is  inevitable,  to  restore  the 
fertility  of  the  soil  by  adding  what  is  required. 

There  has  been,  as  we  have  seen,  much  discussion 
as  to  whether  Liebig  was  right  in  supposing  that  the 
air  does  really  yield  to  the  plants  a  sufficient  supply 
of  nitrogen ;  but  this  is,  after  all,  a  detail,  and  we 
may  say  now,  fifty  years  after  the  first  publication  of 
Liebig's  pioneering  work,  that  nothing  has  been  added 
to,  and  nothing  has  been  taken  from,  the  fundamental 
principles  to  which  he  then  drew  attention,  and  on 
which  he  based  his  theory  of  a  rational  husbandry. 
To-day  Liebig's  teachings  are,  in  their  main  features, 
universally  received.  But,  in  spite  of  his  reputation, 
they  were  not  generally  accepted  by  agriculturists 
when  he  first  announced  them.  Nor  is  this  surprising. 
The  education  of  most  agriculturists  was  then  at 
a  low  point.  Science,  or  what  passed  for  science, 
had  done  very  little  for  agriculture  in  the  past.  The 
difficulties  in  the  way  of  applying  Liebig's  ideas  were 
great,  and  at  first,  owing  to  imperfect  data,  serious 
mistakes  were  made  which  led  to  many  failures. 
Hence  it  was  only  to  be  expected  that  practical  men 
would,  for  a  time,  consider  them  to  be  mere  new- 
fangled notions ;  that  they  should  regard  them  with 
considerable  suspicion,  and  cling  to  the  ideas  and 
practices,  which  were  many  of  them  wise,  handed 


HIS    LIFE    AND   WORK.  107 

clown  by  their  forefathers.  The  publication  of  "  The 
Chemistry  of  Agriculture  and  Physiology  "  only  he- 
ralded, at  first,  a  prolonged  period  of  renewed  experi- 
menting and  warm  discussion.  Liebig  did  not,  however, 
allow  this  to  discourage  him,  but,  for  many  years  after- 
wards, he  devoted  a  large  part  of  his  life  to  studying 
the  practical  application  of  his  theory,  to  gaining  the 
serious  attention  of  practical  agriculturists,  and,  above 
all,  to  bringing  about  such  a  just  appreciation  of  his 
views  as  should  ensure  their  ultimately  being  intelli- 
gently applied  in  practice. 

In  the  first  place,  countless  analyses  of  the  ashes 
of  plants  were  made  at  Giessen  by  Liebig  and  his 
assistants.  These  showed  the  presence  of  different 
minerals  in  every  species,  that  each  species  requires 
from  the  ground  the  same  class  of  salts,  and  hence 
that  it  must  sooner  or  later  exhaust  the  supply  of 
these  salts  in  a  given  plot,  and  render  it  unfit  for  the 
growth  of  the  species  in  question  unless  fresh  supplies 
are  provided. 

Liebig  attempted  to  give  the  necessary  supplies  in 
the  form  of  "  Mineral  Manures,"  and  soon  set  to  work 
to  study  practically  the  effect  of  mineral  manures  on 
a  large  scale.  In  the  year  1845,  previous  experiments 
in  a  garden  having  proved  unsatisfactory,  he  pur- 
chased from  the  town  of  Giessen  about  ten  acres  of 
barren  land — a  sand  pit,  as  he  says,  which  surpassed 
all  the  land  in  the  neighbourhood  in  its  barrenness 
for  ordinary  cultivated  crops ;  in  the  year  this  land 
hardly  grew  so  much  fodder  as  would  have  sufficed 
for  a  single  sheep.  It  consisted  partly  of  sand,  partly 
of  coarse  quartz  and  pebbles,  with  strata  of  sand 
and  some  loam. 

Some  of  the  soil  was  first  tested  by  sowing  it  with 


108  JUSTUS   VON    LIEBIG: 

seeds  in  pots  after  enrichment  with  some  single 
mineral  manure,  with  the  result  that  not  one  of  the 
plants  raised  got  beyond  flowering  ;  this  showed  that 
the  soil  was  bad  enough  for  his  purpose  of  testing  the 
value  of  minerals  as  manure. 

A  number  of  mineral  manures  were  then  prepared 
for  him  according  to  prescriptions  based  on  his  analyses, 
and  these  were  spread  over  the  land  ;  next  he  sowed 
on  different  subdivisions  of  it  wheat,  rye,  barley,  clover, 
potatoes,  turnips,  maize.  In  some  cases  he  added 
sawdust  to  the  manure,  and  in  one  case  he  used  stable 
manure ;  otherwise,  no  ammoniacal  manure  and  no 
mineral  matter  was  employed,  except  that  to  one  plot 
he  applied  some  forest  soil  and  to  another  a  mixture 
of  forest  soil  and  mineral  manure.  Even  in  the  first 
year  he  had  a  harvest ;  the  best  results  were  given  by 
those  plots  in  which  mineral  manures  were  mixed 
with  forest  soil  or  stableyard  manure.  This,  as  he 
says,  enabled  him  to  correct  his  earlier  ideas  of  the 
functions  of  humus,  which  by  its  decay  renders  an 
extra  supply  of  carbonic  acid  gas  to  the  plants  that 
is  especially  valuable  at  the  early  stages.  Gradually, 
without  any  further  supply  of  manure  except  mineral 
manure,  the  land  so  improved  in  productiveness  that 
in  the  fourth  year  his  crops  excited  the  wonder  of  all 
who  had  known  the  original  state  of  it. 

In  1849  this  little  farm  was  purchased  by  his 
gardener,  who  was  then  able  to  farm  it  with  profit, 
raising  some  cattle  on  it  yearly  and  getting  such 
satisfactory  crops  of  corn  that  in  1853  a  neighbouring 
farmer  wrote :  "  With  us  the  wheat  crops  are  very 
poor,  but  on  the  height  (Liebig's  plot)  they  have 
harvested  from  three  fuder  of  rye  twelve  simmer, 
while  I,  from  three  fuder  of  the  best  rye,  have  only 


HIS    LIFE    AND   WORK.  109 

got  five  simmer.     If  you  were  to  see  it,  you  would  be 
astonished ;  it  is  truly  wonderful." 

Of  course,  in  order  to  maintain  the  fertility  of  this 
plot  it  was  necessary  that  the  capital  of  minerals 
introduced  during  the  first  four  years  should  be  care- 
fully husbanded,  and  year  by  year  returned  to  the 
soil  in  the  form  of  the  manure  produced  on  the  farm, 
and  that  little  or  none  of  it  should  be  removed  from 
the  farm  by  selling  the  crops.  Under  these  conditions 
those  ten  acres  of  land  became,  as  it  were,  condensers 
of  carbon  and  nitrogen  from  the  air.  It  was  this 
experiment,  as  well  as  the  estimates  of  ammonia  in 
rain  water,  which  led  Liebig  to  form  the  opinion  that 
it  was  possible,  by  giving  the  soil  proper  physical 
quality  and  composition,  to  bring  about  a  state  of 
things  in  which  sufficient  ammonia  to  maintain  its 
fertility  can  be  collected  or  condensed  from  the  air. 

The  experiment  was,  of  course,  a  costly  one.  It 
rarely  happens  that  an  experiment  is  directly  re- 
munerative, but  it  served  its  purpose  of  testing  the 
agricultural  doctrines  of  Liebig,  and  its  success 
enabled  him,  amid  frequent  difficulties,  to  work 
patiently  in  other  directions. 

One  great  difficulty  was,  as  Yogel  says  in  his 
memorial  address,  "  the  want  of  results "  from  the 
mineral  manures  when  they  were  applied  in  the 
ordinary  course  of  farming.  The  attempt  to  com- 
pensate the  soil  for  the  withdrawal  of  crops  by  the 
addition  of  suitable  mineral  matter  seemed  to  fail, 
because  the  form  in  which  the  salts  were  at  first 
supplied  was  the  wrong  one.  It  was  supposed  that 
if  soluble  salts  or  solutions  of  them  were  applied  to 
the  land,  they  would  be  ineffective  because  they 
would  soon  be  washed  out  of  reach  of  the  roots  of  the 


110  JUSTUS  VON   LIEBIG: 

plants  by  the  rain,  and  therefore  no  pains  was  spared 
in  attempting  to  render  the  mineral  manures  insoluble, 
or,  rather,  so  far  insoluble,  that  the  moisture  in  the 
soil  could  only  gradually  absorb  them  for  the  use  of 
the  plants.  For  this  purpose  suitable  mixtures  were 
first  melted  in  huge  pots,  and  then  ground  to  a  powder 
by  means  of  mills,  before  they  were  put  upon  the  land. 

This  plan  was,  however,  a  brilliant  mistake  which 
a  practical  farmer  might  have  avoided.  For  when 
these  mixtures  were  applied  to  the  soil,  they  were 
found  to  be  almost  without  effect,  or,  at  best,  their 
usefulness  only  showed  itself  after  long  years  of 
delay.  The  single  ingredients  when  applied  alone 
acted,  but  the  same  substances  mixed  would  not  act. 
There  was  evidently  something  wrong. 

Liebig,  convinced  that  the  error  must  be  in  his 
practice,  that  his  hypothesis  was  a  sound  one,  for- 
tunately did  not  allow  this  failure  to  put  an  end  to 
his  experiments,  with  the  result  that  the  failure  led 
him  in  the  end  to  recognise  the  agricultural  import- 
ance of  a  certain  quality  of  the  earth  which  enables 
it  to  protect,  as  it  were,  the  plants  from  being  robbed 
of  their  mineral  food  by  the  rain  as  it  percolates 
through  the  soil.  While  Liebig  was  so  busy  trying  to 
make  his  manures  insoluble,  nature  was  ready  to  do 
it  for  him  in  the  most  suitable  manner. 

It  appears  that  earth  is  capable  of  withdrawing,  to 
some  extent,  soluble  salts  from  their  solutions,  but  the 
importance  of  this  fact — which  had  been  known  for 
some  time — in  relation  to  the  nourishment  of  plants 
was  overlooked  until  about  1850,  when  Liebig's  atten- 
tion was  directed  to  it  through  some  novel  experiments 
made  in  England  by  John  Thomas  Way  on  the 
absorptive  power  of  soils.  Liebig  at  once  recognised 


HIS    LIFE   AND   WORK.  Ill 

their  importance.  Those  who  have  ever  attended  a 
course  of  lectures  on  chemistry  will  remember  that 
many  coloured  solutions,  when  filtered  through  a 
layer  of  finely  divided  animal  charcoal,  lose  their 
colour,  in  consequence  of  the  power  possessed  by  the 
finely  divided  carbon  of  withdrawing  the  coloured  sub- 
stances from  the  solutions.  It  is  possible,  at  any  rate, 
in  some  cases,  to  recover  the  substances  thus  absorbed 
by  charcoal.  Now,  arable  soil  is  in  this  respect  very 
much  like  charcoal.  The  dark  drainings  from  a 
manure  heap,  when  filtered  through  a  layer  of  good 
soil,  flow  away  without  colour  and  without  smell ;  the 
organic  matter,  the  ammonia,  and  the  salts  which  it 
held  in  solution  are  all  more  or  less  completely  with- 
drawn from  it  by  the  soil  The  various  substances  do 
not,  however,  appear  to  be  destroyed,  they  are  held 
by  the  soil  ready  for  the  use  of  plants.  The  discoveries 
made  by  Way  led  Liebig  to  himself  perform  a  series 
of  experiments,  in  which  he  investigated  this  property 
of  "ground  absorption,"  as  it  has  been  called,  by  which 
the  saline  matters  in  the  soil  are  at  once  protected 
from  the  action  of  the  rain  and  held  ready  for 
absorption  by  the  roots  of  plants. 

Liebig's  results,  besides  confirming  the  statements 
of  the  English  observer,  enabled  him  to  declare  at 
last  what  is  the  proper  mode  of  applying  the  mineral 
manures;  they  also  helped  him  to  understand  the 
root  action  of  plants,  and  to  explain  clearly  why  it  is 
that  the  whole  available  quantity  of  a  manure  is  not 
taken  up  by  the  roots  of  the  plants  in  a  single  season. 
Why  it  is,  for  example,  that  if  ten  grains  of  a  phos- 
phate are  taken  up  by  a  crop,  many  times  that  quantity 
must  be  present  in  the  soil  It  is  because  the  roots  of 
a  single  plant  do  not  touch  all  the  soil  about  it,  and 


112  JUSTUS   VON   LIEBIG: 

because  they  only  exhaust  those  parts  with  which 
they  actually  come  into  contact.  Liebig's  excitement 
when  he  recognised  the  effects  of  ground  absorption  was 
very  great.  In  his  writings  at  this  time  he  frankly 
confessed  the  mistake  into  which  he  had  fallen.  This 
new  discovery,  he  declared,  was  like  a  new  life  to  him, 
explaining  as  it  did  all  the  processes  of  agriculture, 
and  why,  whilst  each  single  salt  had  succeeded  as  a 
manure,  combined  they  had  failed. 

Regret  has  sometimes  been  expressed  that  Liebig 
devoted  so  much  valuable  time  and  effort  to  the 
practical  application  of  his  mineral  manures.  It  has 
been  questioned  whether  he  would  not  have  done 
better  if  he  had  left  to  the  practical  farmers  the  duty 
of  applying  the  principles  he  himself  had  traced  out 
for  their  guidance.  Had  he  done  so,  there  can  be  no 
doubt  but  that  he  would  have  saved  himself  much 
annoyance  and  anxiety ;  he  might  even  have  hastened 
the  success  of  his  ideas,  since  it  is  possible  that  a 
practical  farmer  might  have  avoided  the  mistake 
which  led  Liebig  to  spend  so  much  time  in  attempt- 
ing to  render  his  soluble  salts  insoluble. 

But,  on  the  other  hand,  if  Liebig  had  stood  aloof 
from  the  testing  of  his  opinions,  science  and  agricul- 
ture would  alike  have  been  the  poorer — science, 
because  in  that  case  the  full  recognition  of  the  import- 
ance of  ground  absorption  would  almost  certainly 
have  been  delayed;  agriculture,  because  in  his 
practical  work  Liebig  gave  the  agricultural  world  a 
splendid  example  of  what  experimental  agriculture 
ought  to  be,  at  a  time  when  such  an  example  was 
sorely  needed.  Indeed,  when  we  remember  that 
throughout  his  whole  career  Liebig  was  as  greatly 
distinguished  for  his  enthusiastic  services  to  educa- 


HIS   LIFE    AND   WORK.  113 

tion  as  for  his  work  in  pure  and  applied  science, 
and  when  we  consider  his  keen  sense  of  the  urgent 
need  that  farmers  should  play  at  follow  my  leader  no 
longer,  but  learn  how  to  make  their  own  experiments 
on  their  own  farms,  I  do  not  think  we  shall  venture 
too  far  if  we  assume  that  it  was  largely  with  the 
object  of  showing  them  how  this  should  be  done  that 
he  entered  upon  his  labours  in  experimental  agricul- 
ture. However  this  may  be,  no  one  surely  will 
deny  that  the  world  is  greatly  the  richer  for  the 
outcome  of  this  part  of  his  many-sided  activity. 

Liebig  showed  on  many  occasions  his  desire 
that  farmers  should  think  more  for  themselves. 
In  the  preface  to  his  "  Natural  Laws  of  Husban- 
dry," published  in  1863,  he  called  attention  to  the 
fact  that  no  progress  could  be  made  so  long  as 
agriculturists  continued  to  allow  themselves  to  be 
guided  merely  by  the  facts  observed  in  their  own 
neighbourhood,  or  at  most  by  the  system  of  some 
recognised  authority,  and  he  elsewhere  deplored  the 
frequent  existence  of  such  a  state  of  mind  as  that 
which  had  led  a  landowner  to  write  to  the  eminent 
agriculturist,  Thaer :  "  If  I  receive  a  letter  from  you 
this  evening  to  fire  my  buildings,  before  night  they 
shall  be  in  flames." 

In  the  same  book,  writing  on  the  subject  of  farm- 
yard manure,  Liebig  returned  to  this  subject,  and 
after  showing  that  the  rotation  of  crops  which  suits 
one  field  may  not  suit  another  equally  well,  he  said :  "  If 
farmers  would  only  make  up  their  minds  to  acquire 
by  experiments  on  a  small  scale  an  accurate  know- 
ledge of  the  productive  power  of  their  land  for  certain 
kinds  or  classes  of  plants,  a  few  more  experiments 
would  readily  enable  them  to  discover  what  nutritive 


114  JUSTUS   VON    LIEBIG: 

substances  the  land  contains  in  minimum  proportion, 
and  what  manuring  agents  ought  to  be  applied  to 
ensure  the  production  of  a  maximum  crop." 

"  In  matters  of  this  kind,"  said  he,  "  the  farmer 
must  pursue  his  own  course  ...  he  must  not 
put  the  least  faith  in  the  assertion  of  any  foolish 
chemist  who  wants  to  prove  to  him  analytically  that 
his  field  contains  an  inexhaustible  store  of  this  or 
that  nutritive  substance." 

One  cannot  read  this  book  without  perceiving 
that  Liebig's  great  desire  was  not  merely  to  inculcate 
correct  rules  of  husbandry,  nor  to  attempt  to  induce 
the  agriculturists  to  lean  more  on  the  chemists,  but 
to  lead  them  to  take  an  intelligent  interest  in  their 
own  work,  and  to  study  the  bearing  of  science  on  its 
ever-varying  details. 

He  found  most  agriculturists  badly  educated, 
and  either  governed  by  tradition  or  the  slaves  of 
particular  leaders.  They  had  lost  the  power  of  dis- 
tinguishing opinions  from  facts.  They  had  no  idea 
how  to  make  an  experiment.  He  hoped  to  help  to 
put  an  end  to  this  by  inducing  the  rising  generation 
to  take  an  active  part  in  the  attempt  to  apply  scientific 
methods  to  their  art. 

Even  those  who  most  vehemently  dissented  from 
some  of  Liebig's  conclusions  on  special  points  have 
always  admitted  in  the  warmest  terms  the  magnitude 
of  the  service  he  rendered  to  agriculture,  by  the 
masterly  review. of  the  then  existing  knowledge,  and 
by  the  sagacious  generalisations  which  he  brought 
forward  in  his  earlier  works  on  agricultural  chemistry. 
And  when  he  published  his  mature  views  in  1863, 
in  "  The  Natural  Laws  of  Husbandry,"  his  funda- 
mental doctrines  were  already,  in  regard  to  most  of 


HIS    LIFE    AND    WORK.  115 

their  main  features,  generally  accepted.  It  was  then 
no  longer  necessary  that  he  should  demonstrate  the 
errors  of  the  humus  theory,  and,  on  the  other  hand, 
the  true  value  of  humus  was  better  understood. 
In  1863  there  was  no  need  that  he  should  insist 
upon  the  necessit}7  for  mineral  matter  in  the  food 
of  plants,  nor  that  he  should  direct  attention  to 
that  interdependence  of  plants  and  animals,  which 
alone  has  enabled  countless  generations  of  each  class 
to  play  their  parts  in  the  past  history  of  our  globe,  and 
which  alone  makes  the  continued  existence  of  either 
possible.  By  this  time,  also,  the  power  of  arable  soil 
to  withdraw  from  solutions  the  food  materials  most 
essential  to  plants  was  fully  recognised,  and  correct 
views  of  the  action  of  roots  accordingly  had  become 
possible.  In  the  new  book,  therefore,  Liebig  was  able, 
after  many  years  of  experimenting  and  reflecting,  to 
devote  himself  more  especially  to  the  task  of  explain- 
ing how  the  new  knowledge  and  corrected  ideas 
should  be  applied  to  the  practical  objects  of  agri- 
culture. He  could  now  attempt,  in  fact,  to  bridge 
the  gulf  which  had  so  long  separated  science  from 
practice. 

First  among  the  objects  of  the  agriculturist  must 
be  placed  the  maintaining  of  the  permanent  pro- 
ductiveness of  the  soil  To  this  subject  Liebig 
especially  directed  attention  at  this  stage. 

The  following  remarks  will  serve  to  introduce  and 
make  clear  the  last  part  of  Liebig's  teachings  in  agri- 
cultural chemistry  to  which  it  is  possible  to  refer — 
viz.  to  the  tendency  of  the  system  of  farming  adopted 
by  Western  peoples  to  exhaust  the  soil,  and  so  ulti- 
mately to  bring  about  their  own  extinction  or  dispersal 
more  or  less  completely. 


116  JUSTUS   VON   LIEBIG: 

It  must  be  understood  that  a  fruitful  soil  consists 
(1)  of  the  arable  surface  soil,  and  (2)  of  the  subsoil. 
The  former  contains  especially  that  part  of  the  nutri- 
ment of  plants  which  is  held  there  in  consequence  of 
the  absorbing  power  of  humus  * — that  part,  in  fact, 
which  is  immediately  available  for  nourishing  the 
plants.  The  fertility  of  a  soil  depends  on  its  abund- 
ance and  on  its  suitability  for  the  crops  that  are 
to  be  grown. 

The  soil  also  affords  another  source  of  food,  but  in 
this  case  the  food  is  not  immediately  available.  It  is 
stored  up  in  the  form  of  compounds  which  are  not 
soluble  in  water,  and  is  only  gradually  brought  into 
the  available  condition  by  the  process  which  we  call 
"  weathering."  This  process  takes  place  slowly.  It  is 
accelerated  by  the  mechanical  operations  of  agricul- 
ture, in  the  course  of  which  the  insoluble  substances 
are  gradually  disintegrated,  so  that  the  soluble  parts 
slowly  pass  into  solution  under  the  combined  action 
of  air,  water,  and  carbonic  acid  gas.  As  this  saline 
food  is  liberated,  if  the  conditions  are  favourable,  it 
passes  into  what  Liebig  called  a  state  of  "  Physical  t 
combination"  with  arable  soil.  It  then  becomes  an 
immediate  source  of  supply  for  the  use  of  plants. 

Each  soil  has  its  own  degree  of  power  for  absorb- 
ing food,  and  this  constitutes  one  of  the  differences 
between  soils  from  the  agricultural  point  of  view. 
When  manure  is  applied  to  the  surface  of  many  soils, 
most  of  the  food  it  conveys  is  absorbed  by  the  first  few 
inches  of  the  soil,  and  very  little  gets  to  the  subsoil. 

*  Other  constituents  also  contribute  to  ground  absorption, 
notably  oxide  of  iron  and  certain  silicates. 

f  Physical,  because  he  believed  that  the  salts  retain  each  their 
individual  properties. 


HIS    LIFE   AND   WORK.  117 

Consequently,  it  is  difficult  to  replenish  an  exhausted 
subsoil  by  manure.  It  is  advantageous  to  distribute 
the  manure  by  ploughing  or  digging,  and  the  other 
operations  of  the  husbandman,  because,  as  each 
particle  of  the  soil  is  limited  in  its  absorbing  power, 
it  is  only  by  mixing  the  various  parts  that  the  whole 
mass  can  be  brought  to  the  saturated  state  in  which 
it  best  serves  to  nourish  plants.  Evidently,  also,  the 
working  of  the  soil  will  tend  to  an  equal  distribu- 
tion of  the  food  which  is  gradually  set  free  from  the 
insoluble  components  of  the  soil  by  weathering. 

Food  in  the  so-called  state  of  "  physical  combina- 
tion "  is  at  once  available  for  the  use  of  plants, 
because  it  is  not  held  sufficiently  strongly  by  the  soil 
to  resist  the  absorbing  power  of  their  roots.  But 
it  is  retained  firmly  enough  to  prevent  its  rapid  re- 
moval by  the  rain  water  which  percolates  through 
the  soil. 

The  above  facts  enable  us  to  understand  why 
rough  uncultivated  land  will  often  sustain  perennial 
plants  when  it  fails  to  afford  satisfactory  crops  of  the 
summer  plants  grown  by  the  farmer.  The  perennials 
absorb  their  food  at  a  slower  rate  than  the  others,  but 
they  continue  to  absorb  it  for  a  longer  period,  hence, 
they  can  take  advantage  to  a  certain  extent  of  the 
slow  production  of  food  by  weathering ;  they  do  not 
altogether  depend  upon  the  amount  of  food  in  the 
more  readily  available  condition.  But  summer  crops 
must  absorb  quickly.  They  require  far  more  food 
in  their  short  lives  than  the  perennials  need  in  an 
equal  time ;  therefore,  these  only  flourish  on  land  which, 
either  in  consequence  of  prolonged  cultivation,  or  as 
the  result  of  natural  processes,  offers  them  an  ample 
supply  of  immediately  available  food  such  as  is  only 


118  JUSTUS   VON   LIEBIG: 

to  be  found  in  land  that  is  rich  in  "  physically  com- 
bined "  nutriment. 

This,  again,  explains  to  us  the  great  usefulness 
of  weeds  in  waste  places.  Weeds  slowly  accumulate 
food  from  barren  soils ;  and  if  they  are  not  removed, 
by  their  decay  after  death  they  return  this  food  to  the 
soil  in  such  a  form  that  it  enters  into  the  so-called 
"  physically  combined  state."  In  this  way  successive 
generations  of  weeds  gradually  enrich  the  soil,  and 
prepare  it  for  bearing  more  valuable  crops. 

The  fact  that  the  constituents  of  soils  exist  in  the 
two  above-mentioned  forms  makes  it  very  difficult  to 
ascertain  the  value  of  land  by  means  of  chemical 
analysis. 

By  means  of  analysis  the  chemist  can  find  out  for 
the  farmer  how  much  food  of  each  kind  his  soil  con- 
tains— how  much  potash,  how  much  phosphoric  acid, 
and  so  on ;  but  when  it  comes  to  ascertaining  what 
proportion  of  the  various  components  is  in  the 
chemically  combined  state,  and  how  much  in  the 
"  physically  combined,"  or  available  state,  analysis,  in 
Liebig's  time,  broke  down,  and  I  fear  it  must  be  added 
that  it  breaks  down  still.  In  the  early  days,  before  the 
distinction  between  the  available  and  the  unavailable 
food  in  the  soil  had  been  made  clear  to  us,  this 
circumstance  caused  great  confusion,  and  opposed 
a  serious  obstacle  to  progress,  because  the  productive- 
ness of  soils  was  often  found  to  be  apparently  quite 
unconnected  with  their  composition,  which  naturally 
weakened  the  confidence  of  the  farmers  in  the  use- 
fulness of  science  to  their  art. 

We  must  now  pass  to  the  question  of  the  ex- 
haustion of  the  soil  by  the  European  methods  of 
cultivation,  to  which  Liebig  gave  much  consideration. 


HIS    LIFE   AND   WORK.  119 

The  principal  problem  for  agriculture  is  how  to  re- 
place those  substances  which  are  taken  from  the  soil 
by  crops,  and  which  are  not  found  in  the  atmosphere. 
If  the  manure  applied  does  not  replace  what  is 
taken  by  the  crops,  the  fertility  of  a  field,  of  a  farm 
or  of  a  country  will  decrease;  if,  on  the  contrary, 
more  is  given  to  the  field  than  is  taken  away,  its 
fertility  will  increase.  In  a  primitive  state,  a  nation 
of  farmers  who  till  their  ground  well  and  collect  and 
return  to  it  every  trace  of  inanurial  matter  produced 
by  those  who  consume  its  products,  need  not  fear  they 
will  exhaust  their  ground.  The  Japanese  afford  us  an 
example  which  is  to  the  point.  In  Japan  a  teeming 
population  has  been  supported  for  centuries  by  means 
of  a  simple  agriculture,  supplemented  by  fishing. 
This  consists  in  returning  to  the  soil  year  by  year 
all  that  is  taken  from  it  for  food,  except  only  those 
parts  which  pass  into  the  air  and  so  find  their  way 
back  to  the  earth  by  natural  processes. 

The  only  rational  agriculture,  according  to  Liebig, 
would  be  a  system  in  which,  at  least,  everything  that 
is  taken  from  the  land  should  go  back  again.  If  we 
can  enrich  our  soils  from  without,  and  so  add  more 
than  we  take,  so  much  the  better,  provided  that  we 
do  really  enrich  them  by  adding  all  the  necessary 
elements  of  plant  food  in  their  proper  proportions,  and 
do  not  merely  stimulate  the  soil  by  adding  one  or  two 
elements  only,  for  this  cannot  fail  to  ensure  a  premature 
exhaustion  of  those  components  of  the  soil  which  we 
do  not  add. 

This  ideal  of  Liebig's  is  perhaps  reached  in  Japan 
and  by  the  Chinese,  but  not  in  Europe.  In  all 
Western  civilised  countries  a  very  great  part,  and 
sometimes  the  greater  part,  of  the  food  produced  on 


120  JUSTUS  VON   LIEBIG: 

the  land  is  carried  away  to  be  consumed  in  the  towns 
or  in  distant  countries.  Thus  the  greater  part  of  the 
mineral  matter  removed  by  each  crop  is  never  re- 
turned to  the  land.  The  carbon,  the  hydrogen,  and 
some  of  the  nitrogen  are  indeed  ultimately  returned 
through  the  atmosphere,  but,  by  our  systems  of  sewer- 
age, the  mineral  matter  and  a  part  of  the  nitrogen 
are  often  cast  away  and  lost  to  us.  Even  the  carbon 
does  not  go  back  to  the  land  to  pass  through  the 
humus  stage,  and  so  does  not  again  play  its  whole 
part  in  the  processes  which  produce  fresh  supplies 
of  food.  In  China  and  Japan  this  terrible  waste  is 
avoided,  but  not  in  the  West. 

An  ingenious  system  for  staving  off  the  evil 
day  has  made  it  possible  for  European  farmers  to  con- 
tinue to  raise  crops  for  a  long  while.  By  adopting  a 
certain  rotation  of  crops,  by  feeding  animals  on  the 
land  so  as  to  return  a  good  deal  in  the  form  of  manure, 
and  by  importing  food-stuffs  for  their  animals  from 
foreign  countries,  farmers  have  been  able  to  raise 
crops  of  corn,  and  also  meat,  and  to  sell  them  off  their 
farms  without  perceiving  very  obvious  signs  that  the 
land  is  being  permanently  exhausted.  But  what  is  it 
that  really  happens  ? 

If  we  grow  a  crop  of  corn  and  remove  it  from  the 
farm,  the  surface  soil  will  lose  a  certain  portion  of 
the  constituents  that  go  to  the  formation  of  corn. 
These  must  be  returned  in  the  form  of  manure; 
and  if  this  be  done,  the  subsequent  crops  may  reach 
the  level  of  those  first  obtained.  To  provide  this 
manure,  it  is  the  practice  to  grow  such  crops  as 
turnips,  clover,  and  grass,  and  to  feed  cattle  or  sheep  on 
these  on  the  farm.  A  part  of  what  these  cattle  con- 
sume in  their  food  remains  in  their  bodies,  and  this 


HIS    LIFE   AND   WORK.  121 

part,  sooner  or  later,  is  removed  from  the  land,  and, 
except  perhaps  so  far  as  their  bones  are  concerned, 
like  the  <3orn  crop,  is  mostly  lost  to  it.  Another  and 
very  large  portion  of  the  nutritive  substances  drawn 
from  the  land  by  these  creatures  is  returned  to  it  in 
the  form  of  manure,  and  this  enables  the  arable  sur- 
face soil  to  again  support  corn  crops. 

But  it  is  evident  that  the  food  constituents  thus 
supplied  in  the  form  of  manure  to  the  surface  soil 
were  not  created  out  of  nothing  by  the  fodder  plants, 
nor  in  the  bodies  of  the  animals.  There  is  not  the 
slightest  reason  for  supposing  that  this  is  possible. 
The  truth  doubtless  is,  as  Liebig  insisted,  that  the 
deep  penetrating  roots  of  the  fodder  plants  enable 
them  to  extract  nourishment  from  the  subsoil,  which 
is  then  partly  carried  away  and  consumed  in  the  form 
of  milk,  cheese,  meat,  and  partly  restored  to  the 
surface  soil  in  the  manure  provided  by  the  cattle,  to 
be  again  presently  withdrawn  in  the  form  of  corn. 
Only  a  small  part  of  the  nutritive  substances  returned 
in  this  manner  can  ever  reach  the  subsoil  again. 
Most  of  them  will  be  absorbed  by  the  upper  layers, 
whence  they  will  soon  be  carried  off  in  the  subsequent 
corn  crops. 

Under  such  a  system  as  this,  said  Liebig,  the  corn 
crops  may  be  kept  up,  they  may  and  even  do  increase, 
and  this  increase  may  go  on  for  a  long  while  ;  but, 
unless  we  assume  that  the  stock  of  nutritive  matter 
in  the  subsoil  is  infinite,  there  must  be  a  limit. 
Sooner  or  later  the  subsoil  of  each  field,  which  is  thus 
drained  of  its  phosphoric  acid,  potash,  lime,  etc.,  must 
begin  to  lose  its  productive  power  for  the  fodder  crops, 
and  then  the  nutritive  substances  taken  away  from 
the  arable  soil  in  the  form  of  corn  can  no  longer  be 


122  .JUSTUS   VON   LIEBIG: 

returned  to  it  from  the  stores  which  at  first  existed  in 
the  subsoil.  There  are  various  devices  for  delaying 
this  dreadful  consummation,  but  sooner  or  later, 
according  to  the  quality  of  the  subsoil,  exhaustion 
must  ensue,  and  then  the  corn  crops  will  decline,  and 
continue  to  decline,  unless  all  the  mineral  matter,  etc., 
which  is  taken  from  the  soil  be  once  more  returned 
to  it. 

Of  course,  the  progress  of  the  decline  is  slow,  for  the 
store  to  be  drawn  upon  at  first  is  considerable,  and 
the  results  are  only  felt  after  many  generations.  They 
may  be  deferred  by  gathering  fallen  leaves  from  the 
woods,  by  breaking  up  new  ground,  by  drawing  on 
outside  sources  of  manure,  such  as  guano,  etc.,  but  all 
these  methods  are  only  palliatives.  In  face  of  the 
fact  that  corn  can  only  be  grown  if  we  replace  at 
short  intervals  what  each  crop  has  removed  from  the 
surface  soil,  it  is  a  crime  against  human  society,  urged 
Liebig,  to  assume  that  the  fodder  plants  and  the  sub- 
soil are  not  subject  to  the  same  law,  and  that  the 
former  will  constantly  find  in  the  soil  all  the  con- 
ditions of  their  growth. 

To  continue  to  draw  on  the  store  of  mineral 
food  in  the  soil  of  a  farm  without  replacing  it  is 
like  drawing  out  money  from  the  bank  for  daily 
expenses  and  never  troubling  to  earn  any  more  to 
replace  it  before  it  is  all  gone.  Or  rather,  perhaps,  as 
we  are  wasting  a  store  which,  properly  used,  would 
serve  for  the  support  of  untold  future  generations, 
the  system  which  enables  the  farmer  to  sell  successive 
crops  off  his  land  without  returning  their  equivalent 
may  be  compared  to  a  skilfully-contrived  robbery, 
by  which  the  fathers  rob  their  own  children. 

At   present,  owing  to  the   opening  up  of  virgin 


HIS    LIFE   AND   WORK.  123 

soils  in  various  parts  of  the  world,  this  question  has 
seemed  to  become  less  urgent,  for  the  moment,  than  it 
appeared  to  Lie  big,  so  far  as  the  general  population  is 
concerned.  This,  however,  is  but  a  temporary  state 
of  affairs ;  at  best  it  only  gives  us  a  breathing-time. 
The  question  must  be  faced  sooner  or  later.  For  the 
agriculturist  the  problem  how  to  bring  back  to  the 
land  the  nutritive  matter  taken  from  it  to  the  towns 
is  not  one  whit  less  important  now  than  when  Liebig 
wrote.  At  present  we  are  gradually  wasting  a  capital 
which  we  ought  to  make  increasingly  valuable,  and 
which  no  human  power  can  restore  when  once  it  is 
dissipated.  The  problem  is  not  insoluble.  It  has 
been  solved  by  races  we  are  pleased  to  regard  as 
almost  barbarians.  Till  we,  too,  attain  a  solution 
suited  to  our  conditions,  we  remain  mere  robbers  and 
wastrels. 

The  outcome  of  Liebig's  work  in  agriculture  must 
by  no  means  be  measured  solely  by  the  new  facts  and 
new  views  of  facts  contained  in  his  writings.  He  was 
not  only  the  founder  of  a  new  school  of  agricultural 
chemists,  but  so  large  a  proportion  of  the  last  genera- 
tion of  agricultural  chemists  came  directly  or  indirectly 
from  his  school  after  he  laid  down  the  foundations  of 
his  doctrine  that,  without  disparaging  the  valuable 
work  done  by  others — for  example,  by  Boussingault  in 
France  and  by  Lawes  and  Gilbert  in  England — he 
may  almost  be  said  to  be  the  founder  of  agricultural 
chemistry  itself  as  we  know  it  to-day.  And  it  cannot 
be  doubted  that  we  owe  the  existing  machinery 
for  agricultural  research  and  teaching  very  largely 
indeed  to  the  widespread  interest  he  awakened  in 
scientific  husbandry. 

In  his  well-known  address  to  the  CTiemical  Section 


124  JUSTUS  VON  LIEBIG: 

of  the  British  Association,  in  1880,  Dr.  Gilbert  called 
attention  to  this  fact,  when  he  pointed  out  that  it  was 
only  after  the  publication  of  Liebig's  first  reports  to 
the  Association  that  the  Royal  Agricultural  Society 
first  appointed  a  consulting  chemist,  Dr.  Lyon  Playfair 
(now  Lord  Playfair),  Liebig's  pupil,  being  the  first 
holder  of  the  appointment.  Abroad,  both  in  Germany 
and  elsewhere,  numerous  "  agricultural  experimental 
stations"  have  been  established.  These  owe  their 
origin  to  the  teachings  and  influence  of  Liebig.  The 
first  of  them  was  established  at  Mochern,  near  Leipzig, 
in  1851-52.  Twenty-five  years  afterwards  there  were 
seventy-four  such  stations  in  Germany,  sixteen  in 
Austria,  ten  in  Italy,  and  altogether  on  the  Continent 
one  hundred  and  twenty-two.  At  each  of  these  was 
a  chemist,  often  with  one  or  more  assistants.  The 
officials  of  these  institutions  are  charged  with  the 
duty  of  examining  and  reporting  on  such  substances 
as  the  manures,  food-stuffs,  and  seeds  that  come  into 
the  market.  Agricultural  research  has  also  been  a 
characteristic  part  of  their  work.  Their  activity  in 
this  direction  has  covered  a  wide  field.  Whilst  some 
have  occupied  themselves  with  the  study  of  soils, 
manures,  vegetable  physiology,  animal  physiology, 
feeding  experiments,  vine-culture,  wine-making, 
forestry,  and  milk-production,  others  have,  according 
to  their  localities,  specially  investigated  such  subjects 
as  fruit-culture,  olive-culture,  the  utilising  of  bog  and 
peat  land,  or  the  producing  of  silk,  spirits,  etc. 

Besides  this  work  in  Europe,  a  good  deal  is  now 
being  done  in  the  United  States  by  the  workers  in 
numerous  agricultural  stations. 

In  Great  Britain  much  less  has  been  done  than 
abroad.  Neither  the  State,  nor  the  great  landowners 


HIS    LIFE    AND    WORK.  125 

as  a  class,  have  taken  the  lead  in  the  matter — with 
the  result  that  a  few  years  ago  the  German  Empire 
already  possessed  above  one  hundred  high  schools, 
middle  schools,  and  lower  schools,  with  a  full  pro- 
vision of  experimental  stations  attached  to  them, 
besides  more  than  a  thousand  others  where  the 
principles  of  agriculture  were  taught  to  all  classes; 
whilst  there  were  in  England  at  the  same  time  only 
two  agricultural  colleges,  one  each  hi  Scotland  and 
Ireland,  with  a  laboratory  of  agricultural  chemistry 
in  London  for  higher  students,  and  South  Kensington 
courses  for  those  of  a  lower  grade.  Since  that  time 
there  is  reason  to  hope  that  a  happier  state  of  things 
has  been  started  by  the  County  Councils.  But  there 
is  still  much  lee-way  to  make  up,  and  not  only  are 
our  farmers  terribly  below  Liebig's  ideal  of  a  race  of 
husbandmen  acquainted  with  the  principles  of  their 
art  and  capable  of  intelligently  applying  them,  but 
their  opportunities  of  getting  the  scientific  training 
and  knowledge,  which  alone  can  cure  the  present  evil 
state  of  things,  are  still  terribly  insufficient. 


126  JUSTUS   VON   LIEBIG: 


CHAPTER  VII. 

PHYSIOLOGICAL   CHEMISTRY. 

Origin  of  Animal  Heat— Classification  of  the  Components  of 
Food — Plants  elaborate  the  Nitrogenous  Components  for 
Tissues  of  Animals — Importance  of  Albumin  in  Food  of 
Animals — Use  of  the  Non-nitrogenous  Components  of  Food 
— Liebig's  Classification  of  Food-Stuffs  into  the  "Plastic  Foods" 
and  "  Respiratory  Foods  " — "  Plants  accumulate  Force  "- 
Origin  of  Animal  Fat — Bischoff  on  Liebig's  Contributions  to 
Physiology — Relation  of  Nitrogenous  and  Non-nitrogenous  Food 
to  Work — Method  of  Studying  Production  of  Urea  in  the 
Organism — Motions  of  the  Juices  in  the  Animal  Body — Re- 
searches on  Flesh,  Creatine,  Creatinine,  Sarcosine,  etc. — Mineral 
Matter  in  Flesh  and  Blood — Chemistry  of  the  Cooking  of  Flesh 
— Extract  of  Meat — Vital  Force — Objects  of  Liebig  in  his 
Physiological  Work. 

LIEBIG  was  very  conscious  of  the  vast  importance 
of  physiological  studies,  and  at  one  time  he  even 
contemplated  occupying  himself  with  medicine ;  and 
though  this  idea  was  never  carried  out,  a  great  part 
of  his  life  was  devoted  to  efforts  to  advance  medical 
science  through  physiology.  His  first  work  on  animal 
chemistry  constituted  the  second  part  of  his  Report 
to  the  Chemical  Section  of  the  British  Association,  in 
1842.  In  it  he  traced  the  applications  of  organic 
chemistry  to  animal  physiology  and  pathology. 

Just  as  Lavoisier  during  the  latter  half  of  the 
previous  century  had  laid  the  foundation  of  what 
may  almost  be  called  a  new  science,  by  the  success 
with  which  he  applied  to  chemistry  methods  that 


HIS    LIFE    AND    WORK.  127 

had  long  before  been  employed  in  physics — that 
is,  the  use  of  weights  and  measures* — so  Liebig 
aimed  at  applying  the  new  and  altered  views  that  had 
been  introduced  into  organic  chemistry  to  the  elucida- 
tion of  the  problems  of  physiology  and  pathology. 
Ideas  derived  from  chemistry  had  previously  often 
been  successfully  applied  to  the  problems  presented 
by  the  medical  art.  But  for  some  time  before  Liebig 
directed  his  attention  to  physiology,  physiologists 
had  concerned  themselves  especially — perhaps  almost 
exclusively — with  the  study  of  the  forms  of  organised 
bodies  and  of  the  phenomena  of  motion  within  them, 
whilst  the  study  of  the  uses  and  functions  of  the 
different  organs  and  of  their  mutual  connection  in  the 
animal  body  had,  to  a  great  extent,  fallen  into  the 
background.  Their  researches  had  given  most  valuable 
results,  but  they  yielded,  as  it  seemed  to  Liebig,  no 
conclusions  calculated  to  give  a  real  insight  into  the 
vital  processes.  And  it  appeared  to  him  that  the 
greatest  hope  of  advance  in  this  direction  was  to  be 
found  in  once  more  making  chemistry  the  handmaid 
of  physiology. 

It  was  natural  that  Liebig,  the  great  master  of 
organic  chemistry,  should  apply  himself  to  the  task 
of  bringing  the  new  organic  chemistry  into  the  service 
of  the  sister  science. 

A  hundred  and  fifty  years  ago,  chemistry  and 
physics  had  comparatively  little  in  common.  A 
hundred  years  afterwards  it  had  become  difficult 
to  draw  a  line  between  them ;  Liebig  looked  for- 
ward to  the  time  when  chemistry  and  physiology 

*  Lavoisier  did  not  introduce  the  use  of  the  balance  into  chemistry, 
as  has  often  been  stated.  No  one,  however,  advanced  chemistry  by 
the  use  of  this  instrument  so  much  as  he  did. 


128  JUSTUS   VON   LIEBIG: 

would  similarly  be  so  fused  together,  as  it  were,  as 
to  make  it  difficult  to  clearly  separate  the  one  from 
the  other.  "  In  the  hands  of  the  physiologist,"  he 
says,  "  organic  chemistry  must  become  an  intellectual 
instrument  by  means  of  which  he  will  be  enabled 
to  trace  the  causes  of  phenomena  invisible  to  the 
bodily  sight."  It  was  the  use  of  this  new  instrument 
that  he  wished  to  illustrate  by  his  "  Organic  Chem- 
istry in  its  Applications  to  Physiology  and  Pathology." 
The  production  of  this  book  provoked  at  least  as 
much  interest,  and  even  more  opposition,  than 
his  writings  on  agriculture.  This  was  probably  due, 
not  only  to  what  he  said,  but  often  very  largely  to 
how  he  said  it.  For  it  must  be  confessed  that  Liebig 
was  severe  upon  what  he  regarded  as  the  neglect  by 
physiologists  of  the  quantitative  methods  which  had 
for  some  time  been  in  use  in  chemistry. 

Even  before  Liebig's  great  contributions  to  physio- 
logical chemistry  were  published,  there  was  evidence 
that  the  reign  of  the  empirical  method  in  medicine  was 
coming  to  an  end.  The  rapid  progress  of  chemistry, 
and  especially  of  organic  chemistry,  could  not  fail  to 
attract  the  attention  of  physiologists,  and  it  conveyed 
to  them  the  lesson  that  the  true  path  of  advance  is 
through  the  combined  employment  of  experiment  and 
observation. 

When  it  is  observed  that  a  lean  goose  weighing 
four  pounds  gains  in  a  few  weeks  three  and  a  half 
pounds  of  fat  from  the  consumption  of  twenty-four 
pounds  of  maize,  the  observation,  taken  by  itself, 
might  well  lead  us  to  conclude  that  the  twenty -four 
pounds  of  maize  contained  in  them  three  and  a  half 
pounds  of  fatty  matter.  At  the  best  it  leaves  the  question 
completely  open  whether  a  goose  can  produce  any  fat 


HIS   LIFE    AND   WORK.  129 

from  the  non-fatty  substances  in  its  food.  But  if  we 
appeal  to  an  experiment,  if  we  feed  the  goose  on  food 
of  known  composition — that  is  to  say,  if  we  analyse 
samples  of  the  food,  and  find  that  the  amount  of 
fat  in  the  food  eaten  is  considerably  less  than  that 
which  is  accumulated  by  the  goose,  we  shall 
definitely  settle  the  question.  Similarly,  by  varying 
the  composition  of  the  food  administered  to  our 
goose,  we  might  hope  to  decide  which  of  its  com- 
ponents was  the  source  of  the  fat  produced.  By 
similar  experiments  on  other  animals  it  would  become 
possible  to  decide  the  question  whether  or  not  fat  can 
be  produced  in  the  animal  body  from  carbohydrates. 
Here  we  have  a  simple  illustration  of  the  experi- 
mental method  as  it  may  be  applied  to  physiology. 

During  the  decade  which  preceded  the  appearance 
of  Liebig's  book,  there  had  been,  as  said  above, 
distinct  indications  that  some  physiologists  per- 
ceived a  new  road  opening  before  them.  Johannes 
Miiller  and  Tiedemann,  for  example,  had  already  ex- 
pressed themselves  in  support  of  the  experimental 
method,  and  in  1841  Bischoff  had  perceived,  with 
prophetic  vision,  that  the  direction  which  organic 
chemistry  was  then  taking  was  of  the  greatest  im- 
portance to  physiology,  and  in  this  connection  he  had 
already  recognised  the  value  of  Liebig's  work.  More- 
over, various  useful  steps  had  been  taken.  In  spite 
of  the  almost  universal  reluctance  of  investigators 
before  Liebig's  time  to  abandon  the  idea  that  in 
biological  processes  all  manifestations  of  chemical  and 
physical  action  are  in  some  mysterious  way  modified 
and  overruled  by  a  special  vital  force,  Wohler,  as 
we  have  seen,  had  weakened  their  hold  on  this  idea 
by  producing,  from  mineral  sources,  urea,  a  most 


130  JUSTUS  VON   LIEBIO: 

characteristic  product  of  animal  life.  Prout  had 
observed  the  presence  of  hydrochloric  acid  in  the 
stomach,  Gmelin  and  Tiedemann  had  investigated 
the  processes  of  digestion,  Wohler  had  observed 
that  salts  of  organic  acids  in  passing  through  the 
animal  body  are  converted  into  carbonates — that  is, 
into  the  very  substances  which  they  would  form  if 
consumed  in  combustion — and  many  other  isolated 
but  valuable  contributions  to  animal  chemistry  had 
been  made. 

Thus,  when  Liebig  turned  his  mind  to  the  study  of 
the  chemistry  of  physiology,  he  found  a  mass  of  facts 
ready  to  his  hand,  and,  above  all,  a  soil  which  was  not 
altogether  unprepared  to  receive  his  ideas.  Whilst, 
in  addition,  his  great  authority  as  an  organic  chemist 
made  him  secure  of  an  audience  which  extended  even 
far  beyond  the  ranks  of  those  engaged  in  the  study  of 
science  and  its  applications.  It  was,  therefore,  under 
auspicious  conditions  in  every  respect  that  he  at- 
tempted the  task  of  elucidating  the  action  of  chemical 
and  physical  laws  in  the  life-processes  of  animals. 

The  most  generally  interesting  and  most  wide- 
reaching  of  all  Liebig's  teachings  in  physiological 
chemistry  are  doubtless  those  which  deal  with  the 
relations  of  plants  and  animals  to  each  other  and  to 
their  environment.  These  relationships  have,  how- 
ever, already  been  partly  discussed  in  the  chapter  on 
agricultural  chemistry ;  and  therefore,  before  returning 
to  them,  it  will  be  best  to  illustrate  his  physiological 
work  by  examples  of  his  treatment  of  some  of  the 
more  important  questions  which  go  to  make  up  the 
subject.  I  select  for  this  purpose  not  simply  those 
questions  on  which  his  conclusions  are  still  accepted 
as  true,  nor  those  on  which  his  opinions  have  become 


HIS   LIFE    AND   WORK.  131 

truisms,  but  rather  those  which  will,  on  the  whole, 
convey  the  clearest  idea  of  the  scope  and  method  of 
his  work  to  readers  who  are  not  already  acquainted 
with  this  branch  of  science. 

One  of  the  most  interesting,  and  one  of  the  most 
important,  questions  which  Liebig  examined  was  that 
of  the  origin  of  the  heat  of  the  animal  body. 

The  temperature  of  every  human  being  in  a  good 
state  of  health  may  be  said  to  be  practically  constant. 
It  only  varies  during  the  twenty-four  hours  from 
36-5°  to  37-5°  C.  (98°  to  99°  F.) ;  and  so  it  is  with  many 
other  animals,  including  most  mammals  and  birds.* 
The  temperature  varies  a  little  in  different  parts  of 
the  body;  it  is  a  little  higher  internally  than  ex- 
ternally, for  example.  This  uniformity  of  temperature 
is  maintained  in  spite  of  the  fact  that  a  constant  loss 
of  heat  occurs  by  radiation,  evaporation,  and  the  ex- 
pulsion of  warm  air  from  the  lungs  in  expiration,  etc. 
From  the  data  given  in'  Professor  HaUiburton's 
"Chemical  Physiology"  I  have  calculated  that  a 
human  being  in  a  state  of  rest  loses  enough 
heat  in  twenty-four  hours  to  melt,  approximately, 
sixty-six  pounds'  weight  of  ice.  What  is  the  source 
of  all  this  heat,  which  from  one  person,  in  the  course 
of  a  long  life,  would  suffice  to  melt  a  small  iceberg  ? 
By  what  processes  is  it  generated  ? 

Long  before  Liebig's  time  Lavoisier  perceived 
the  analogy  between  the  processes  of  combustion 
and  respiration;  for  both  of  them  air  is  required, 
and  by  both  of  them  carbonic  acid  gas  is  formed. 
Lavoisier  had  suggested  in  a  paper,  published  jointly 
with  Laplace,  that  the  heat  evolved  by  the  animal 

*  Even  the  cold-blooded  animals  have  a  temperature  slightly  above 
that  of  their  environment. 


132  JUSTUS  VON  LIEBIG: 

organism  corresponds  to  the  heat  of  combustion  of 
the  carbon  and  hydrogen  which  are  taken  into  the 
body  in  the  form  of  food,  and  they  had  made 
some  experiments  on  the  subject.  Subsequently 
this  heat  was  measured  with  the  greatest  degree 
of  exactness  then  attainable.  The  results  showed 
that  whilst  the  explanation  of  Lavoisier  and  Laplace 
would  account  for  the  greater  part  of  the  heat 
given  out  by  animals,  it  would  not  account  for  the 
whole  of  it;  about  10  or  11  per  cent,  remained, 
which,  it  seemed,  could  not  have  come  from  the 
Combustion  of  the  food. 

The  mental  attitudes  of  the  older  school  of  physio- 
logists, and  of  Liebig  and  his  successors,  are  well 
illustrated  by  their  respective  methods  of  treating 
the  problem  which  was  thus  introduced,  and  which 
urgently  demanded  an  answer. 

The  older  school  accepted  the  result,  and  at  once 
proceeded  to  invent  a  theory  to  account  for  it.  They 
suggested  new  sources  of  heat,  such  as  nervous 
actions,  or  friction  within  the  animal  organism. 

Liebig,  on  the  other  hand — though  then  unaware, 
it  is  said,  of  the  principle  of  the  conservation  of 
energy — perceived  the  emptiness  of  these  theories, 
which  only  raised  new  difficulties.  He,  therefore, 
carefully  reconsidered  the  whole  subject;  and  when 
he  found,  after  correcting  the  calculations  in  certain 
respects,  that  a  surplus  there  surely  was,  proceeded  at 
once  to  search  for  a  possible  source  of  error  in  the 
experiments  themselves.  He  found  such  a  source  of 
error  in  the  fact  that  the  calorimeter  *  employed  was 

*  A  calorimeter  is  an  instrument  for  measuring  "  quantities  of 
heat."  A  unit  of  heat  may  be  taken  to  be  that  quantity  which  will 
raise  one  gram  of  water  from  0°  to  1°  C. 


HIS    LIFE   AND   WORK.  133 

one  in  which  the  animals  experimented  on  might 
very  conceivably  have  been  cooled  below  their  initial 
temperature,  so  that  the  heat  taken  up  and  recorded 
by  the  instrument  might  very  possibly  not  have  been 
derived  solely  from  the  respiration  of  the  animal ; 
part  of  it  might  have  been  due  to  the  cooling  of  its 
body.  In  summing  up  his  views  on  this  subject,  he 
declared  himself  to  be  finally  convinced  that  the  whole 
of  the  sensible  heat  produced  in  an  animal  body 
could  be  accounted  for  by  the  processes  of  oxidation 
which  occur  within  the  organism. 

To-day  the  correctness  of  Liebig's  decision  is  so 
completely  established  that  it  may  be  regarded  as 
one  of  the  truisms  of  science.  Whilst  we  now 
certainly  admit  that  friction,  nervous  activity,  etc., 
may  actually  give  rise  to  heat,  we  recognise  that  these 
actions  themselves  are  only  intermediate  steps,  as  it 
were,  between  the  chemical  changes  concerned  and 
the  heat  ultimately  measured,  and  that,  therefore,  heat 
from  such  sources  could  not  lead  to  the  production  of 
more  heat  by  the  life  process  of  the  animal  than  that 
which  corresponds  to  the  chemical  changes  which 
occur  within  it. 

But  Liebig's  conclusion  was  by  no  means  accepted 
at  once  by  his  contemporaries.  At  first  they  rose  up 
against  him,  and  said  it  was  not  true.  The  physicians 
thought  they  had  discovered  special  sources  of  heat 
in  the  animal  body.  Even  the  chemists  did  not 
support  him.  Berzelius  wrote,  near  the  end  of  a 
well-known  letter  on  the  subject :  "  You  will  easily 
see,  my  dear  Liebig,  that  you  are  here  standing 
on  hollow  ground,  and  that  whatever  you  build 
must,  in  spite  of  your  talent,  sooner  or  later  fall 
to  pieces."  Afterwards,  when  it  had  become  plain 


134  JUSTUS  VON  LIEBIG: 

that  Liebig  was  right,  some  of  his  opponents  de- 
clared that,  though  his  conclusion  was  true,  it  was 
not  new,  but  only  what  Lavoisier  and  Laplace 
.  had  said  before  him.  This  was  true  enough 
in  a  sense,  but  it  was  unfair.  For,  as  BischofF  has 
pointed  out,  Liebig  by  no  means  merely  developed 
the  idea  of  his  predecessors.  His  merit  is  that  he 
found  false  doctrines  generally  accepted,  and  over- 
threw them  almost  single-handed  in  the  face  of  the 
strongest  opposition. 

In  some  of  his  most  important  contributions  to 
physiology,  Liebig  discussed  the  classification  of  foods, 
and  dealt  generally  with  the  chemistry  of  the  food  of 
animals. 

The  components  of  plants  on  which  animals  feed 
include,  besides  a  small  amount  of  mineral  matter, 
two  great  classes  of  organic  compounds — first,  the 
non-nitrogenous  substances,  such  as  the  carbohydrates, 
sugar,  starch,  and  cellulose,  together  with  fats ;  secondly, 
the  nitrogenous  compounds,  of  which  the  most  im- 
portant are  the  albuminoids.  The  gluten  of  flour, 
vegetable  albumin,  and  vegetable  casein,  which  occurs 
especially  in  the  seeds  of  peas,  beans,  and  similar 
plants,  belong  to  the  nitrogenous  group  of  substances. 

Liebig's  attention  having  been  drawn,  through  the 
writings  of  Mulder,  to  the  similarity  between  the  nitro- 
genous constituents  of  plants  and  animals,  and  to  the 
probability  that  animals  depend  upon  plants  for  these 
substances,  and  are  themselves  unable  to  form  them, 
he  and  his  pupils  re-examined  these  substances.  They 
found  that  the  nitrogenous  compounds  which  form  the 
main  part  of  the  nitrogenous  food  of  the  graminivorous 
animals  are  indeed  composed  of  the  same  chemical 
elements — viz.  carbon,  hydrogen,  oxygen,  nitrogen, 


HIS    LIFE   AND   WORK.  135 

with  a  little  sulphur  and  phosphorus,  united  in  very 
nearly  the  same  proportions  by  weight  as  those  which 
are  present  in  animal  fibrin,  and  in  the  other  albumin- 
ous constituents  of  the  blood.  Their  properties  were 
also  examined,  and,  so  far  as  could  be  then  ascer- 
tained, the  two  classes  of  substances  were  found  to 
correspond  closely  in  their  chief  qualities.  They  were 
not  different  substances  with  the  same  composition, 
but  actually  identical,  or  nearly  identical,  com- 
pounds. 

Now,  the  graminivorous  animals,  as  we  all  know, 
form  a  link  between  the  plants  which  they  eat  and 
the  flesh-eating  animals — in  which  class,  for  con- 
venience, we  may  include  man — which  eat  them  ; 
consequently  this  discovery  threw  floods  of  light  on 
the  mutual  relations  of  the  plant  and  animal  kingdoms 
of  nature. 

Since  vegetable  albumin  and  fibrin  are  so  little 
different  from  animal  albumin  and  animal  fibrin,  it 
seems  to  follow  that  the  vegetables  produce  in  their 
organism,  as  it  were,  the  blood  of  the  animals. 

It  is  well  known  that  nitrogenous  food-stuffs  are 
absolutely  essential  for  the  well-being  of  animals ; 
the  flesh-eating  animals  in  consuming  the  flesh  of 
herb  -  eaters  consume,  strictly  speaking,  only  the 
vegetable  principles  which  have  first  served  for 
nourishing  the  latter.  Vegetable  albumin  and  fibrin, 
in  short,  according  to  Liebig,  play  a  similar  part  in 
nourishing  the  herb-eating  animals  as  that  which 
the  animal  fibrin  and  albumin  play  in  nourishing 
the  flesh-eaters.  It  follows  that  the  growth  and 
development  of  all  animals  are  dependent  on  their 
receiving  certain  substances  from  the  plants  iden- 
tical, or  nearly  identical,  in  composition  and  in  their 


136  JUSTUS   VON   LIEBIG: 

general  properties  with  the  chief  constituents  of  the 
blood  of  the  animals  themselves. 

In  this  sense,  Liebig  taught  that  the  animal 
organism  gives  to  the  blood  only  its  form,  that  it 
is  incapable  of  creating  blood  except  out  of  substances 
which  already  contain  its  chief  constituents,  in  the 
form  of  compounds  closely  allied  to  those  which 
occur  in  the  blood  itself.  Liebig  did  not  mean  that 
the  animal  organism  cannot  produce  new  compounds 
from  its  food,  for  it.  was  well  known  that  an  extensive 
variety  of  compounds  do  result  from  the  life  processes 
of  animals,  but  that  the  organism  depends  for  its 
starting-point  on  certain  substances  in  the  blood 
which  are  so  much  like  the  albuminoids  of  plants 
that  at  Liebig's  time  they  were  practically  indistin- 
guishable, so  that  as  far  as  the  albuminoids  are 
concerned,  the  development  of  the  animal  begins 
where  the  life  of  the  plant  ends.  From  this  point  of 
view,  the  plant  holds  an  intermediate  position  between 
the  mineral  and  animal  worlds.  The  animal  is  in- 
capable of  assimilating  the  compounds  stored  up  in 
inorganic  nature.  To  render  them  fit  for  the 
support  of  the  animal,  they  must  undergo  a  course 
of  preparation  in  the  plant,  in  which  process  the 
simple  stable  molecules  of  the  mineral  substances  are 
converted  into  more  complex  and  less  stable  molecules 
of  a  higher  order,  from  which  may  afterwards  be  built 
up  the  yet  more  complex  and  yet  more  instable  sub- 
stances which  are  capable  of  doing  service  in  forming 
and  maintaining  the  life  of  the  animal. 

The  main  pillar  of  this  great  generalisation,  which 
we  owe  to  the  work  of  Liebig  and  Mulder,  consists  in 
the  fact  just  quoted — viz.  in  the  identity,  or,  to  be 
more  correct,  in  the  close  chemical  similarity  between 


HIS    LIFE   AND   WORK.  137 

the  nitrogenous  compounds  found  in  plants  and  those 
which  occur  in  the  blood  of  animals. 

Liebig  illustrated  the  importance  of  the  albumin- 
ous substances  to  animal  life  by  calling  attention  to 
the  changes  in  which  a  chick  develops  from  an  egg. 
Both  the  white  of  egg  and  the  yolk  are  largely 
composed  of  albuminoids.  An  egg,  after  impregna- 
tion, if  maintained  at  a  suitable  temperature,  with 
the  aid  of  the  oxygen  of  the  air,  which  finds  ready 
access  through  the  porous  shell,  gradually  develops 
all  the  parts  of  the  animal  body — feathers,  claws, 
membranes,  fibrin,  blood-vessels,  nerves,  and  so  on. 
In  the  process,  all  the  albumin  disappears.  Evidently 
albumin  is  the  foundation,  he  said,  of  the  whole  series 
of  peculiar  tissues  which  constitute  those  organs 
which  are  the  seat  of  vital  actions.  The  elements  of 
these  organs,  which  now  possess  form  and  vitality, 
were  originally  elements  of  albumin. 

The  results  of  examining  other  alimentary  sub- 
stances always  told  the  same  tale ;  he  found  albumin 
— or,  at  least,  those  bodies  closely  allied  to  it,  which  I 
have  called  albuminoids — present  in  every  food,  which 
by  itself  suffices  to  support  animal  life. 

What  we  call  "  meat " — that  is,  the  muscle  of 
herbivora — is  very  largely  composed  of  solid  albu- 
minoids. 

If  we  examine  milk,  the  food  prepared  in  the 
body  of  the  mother  for  the  nourishment  of  her 
young,  we  shall  find  in  it,  besides  a  kind  of  sugar, 
fat,  and  a  little  albumin,  a  substance  called  casein. 
Now  casein  is  nearly  identical  in  composition  with 
the  albuminous  constituents  of  blood  fibrin  and 
albumin,  and  also  analogous  in  its  nature  to  the 
vegetable  casein  found  in  peas  and  beans.  The 


138  JUSTUS   VON   LIEBIG: 

young  animal,  therefore,  receives  in  this  form  the 
albuminous  material,  which  provides  it  with  the 
fundamental  constituents  of  its  blood,  from  which 
its  flesh,  bones,  and  nerves  must  be  elaborated. 

Again,  eggs,  which  are  so  rich  in  albuminous 
matter,  in  a  form  very  ^favourable  to  its  complete 
absorption,  will,  even  by  themselves,  support  life ;  and 
cheese,  which  contains  both  the  fat  and  the  casein  of 
milk,  would  doubtless  do  still  better  if  it  were  equally 
digestible ;  but  a  diet  of  fat,  let  us  say  of  butter  or 
of  starch,  or  of  butter  and  starch  together,  soon  leads 
to  starvation.  This  we  can  well  understand  aided  by 
the  light  which  Liebig  has  thrown  on  the  subject.  Fat 
and  starch  are  non-albuminous  substances;  albuminous 
material  must  be  provided  in  our  food  to  secure  the 
production  of  blood,  and  therefore  blood  cannot  be 
formed  from  a  diet  consisting  of  fat  and  starch  alone. 
That  is  why  these  foods  will  not  by  themselves 
support  life. 

Albuminous  material,  then,  must  be  present  in  the 
food  of  animals;  they  cannot  produce  it  for  them- 
selves, though  they  may  modify  it ;  they  depend  upon 
the  plants  for  a  supply  of  it,  and  those  parts  of  plants 
which  contain  a  good  proportion  of  albuminous  matter 
will,  if  digestible,  generally  be  found  more  nutritive 
than  those  which  contain  very  little. 

In  the  "  Familiar  Letters  on  Chemistry  "  (p.  350) 
Liebig  summed  up  his  views  in  1851  in  the  following 
oft-quoted  passage  : — 

"  How  admirably  simple,  after  we  have  acquired  a 
knowledge  of  this  relation  between  plants  and  animals, 
appears  to  us  the  process  of  formation  of  the  animal 
body,  the  origin  of  its  blood  and  of  its  organs !  The 
vegetable  substances  which  serve  for  the  production 


HIS    LIFE    AND    WORK.  139 

of  blood  contain  already  the  chief  constituent  of 
blood  ready  formed,  with  all  its  elements.  The  nutri- 
tive power  of  vegetable  food  is  directly  proportional 
to  the  amount  of  these  sanguigenous  compounds  in  it ; 
and,  in  consuming  such  food,  the  herbivorous  animal 
receives  the  very  same  substances  which,  in  flesh, 
support  the  life  of  the  carnivora. 

"  From  carbonic  acid,  water,  and  ammonia— that  is, 
from  the  constituents  of  the  atmosphere — with  the 
addition  of  sulphur  and  of  certain  constituents  of  the 
crust  of  the  earth,  plants  produce  the  blood  of  animals ; 
for  the  carnivora  consume,  in  the  blood  and  flesh  of 
the  herbivora,  strictly  speaking,  only  the  vegetable 
substances  on  which  the  latter  have  fed.  These  nitro- 
genised  and  sulphurised  vegetable  products,  the  albu- 
minous or  sanguigenous  bodies,  assume,  in  the  stomach 
of  the  herbivora,  the  same  form  and  properties  as  the 
fibrin  of  flesh  and  animal  albumin  do  in  the  stomach 
of  the  carnivora.  Animal  food  contains  the  nutritive 
constituents  of  plants  stored  up  in  a  concentrated 
form. 

"  A  comprehensive  natural  law  connects  the  de- 
velopment of  the  organs  of  an  animal,  their  growth 
and  increase  in  bulk,  with  the  reception  of  certain 
substances,  essentially  identical  with  the  chief  con- 
stituents of  its  blood.  It  is  obvious  that  the 
animal  organism  produces  its  blood  only  in  regard 
to  the  form  of  that  fluid,  and  that  nature  has  denied 
to  it  the  power  of  creating  blood  out  of  any  other 
substances,  save  such  as  are  identical  in  all  essential 
points  with  albumin,  the  chief  constituent  of  the 
blood. 

"  The  animal  body  is  a  higher  organism,  the  de- 
velopment of  which  begins  with  those  substances 


140  JUSTUS   VON   LIEBIG: 

with  the  production  of  which  the  life  of  those  vege- 
tables ends  which  are  commonly  used  for  food.  The 
various  kinds  of  grain  and  of  plants  used  for  fodder 
die  as  soon  as  they  have  produced  seeds.  Even  in 
perennial  plants  a  period  of  their  existence  terminates 
with  the  production  of  their  fruit.  In  the  infinite  series 
of  organic  products  which  begins  with  the  inorganic 
food  of  plants,  and  extends  to  the  most  complex  con- 
stituents of  the  nervous  system  and  brain  of  animals, 
the  highest  in  the  scale,  we  see  no  blank,  no  interrup- 
tion. The  nutritive  part  of  the  food  of  animals,  that 
from  which  the  chief  material  of  their  blood  is 
formed,  is  the  last  product  of  the  productive  energy  of 
vegetables." 

The  vegetable  matters  which  the  graminivorous 
animals  consume  are  not,  however,  entirely,  or  even 
chiefly,  composed  of  albuminous  substances,  and  in 
some  of  them  the  proportion  of  albuminoids  is  very 
small. 

The  non-nitrogenous  components  of  vegetables 
may  be  divided  into  mineral  matter — the  carbo- 
hydrates— which  occur  in  relatively  large  quantities 
almost  invariably,  and  fats,  which  are  usually  .present 
in  small  or  decidedly  moderate  proportions.  It  is 
found  that  a  large  part  of  these  organic  materials  can 
be  absorbed  and  made  useful  by  animals ;  the  fibre 
of  vegetables  is  to  a  great  extent  rejected,  however, 
especially  the  coarser  parts,  but  such  components 
as  starch  and  sugar  are  readily  absorbed,  and  are 
very  useful.  The  carbohydrates  and  the  fats  contain 
only  carbon,  hydrogen,  and  oxygen ;  they  contain  no 
nitrogen,  no  sulphur,  no  phosphorus. 

The  food  of  the  carnivora  also  contains  a  certain 
amount  of  non-albuminous  matter.  Flesh  contains  a 


HIS    LIFE   AND   WORK.  141 

variable  quantity  of  fat,  and  niilk  also  contains  fat 
(from  which  comes  butter),  and  with  it  a  cry  st  alii  sable 
substance  called  sugar  of  milk,  which  belongs  to  the 
class  of  compounds  called  the  carbohydrates.  (See 
p.  85.) 

The  relative  proportions  in  which  the  albuminoids, 
fat,  and  sugar  occur  in  milk  are  not  constant,  and 
similarly  the  proportions  which  albuminoids  bear 
to  the  other  constituents  of  flesh  and  of  vegetables 
vary  considerably  in  different  specimens.  Thus  oats, 
on  an  average,  contain  about  65  per  cent,  of  carbo- 
hydrates and  fibre,  and  about  12  per  cent,  of 
albuminoids,  but  a  given  sample  of  oats  would  pro- 
bably be  found  to  have  rather  more  or  rather  less 
than  this  proportion  of  albuminoids  or  of  carbo- 
hydrates. 

These  facts  lead  us  to  Liebig's  celebrated  classifi- 
cation of  the  food  of  men  and  animals.  "  The  food 
of  men  and  animals,"  he  said,  "  consists  of  two 
classes  of  substances  essentially  different  in  their 
compositioa" 

"  The  one  class,  consisting  of  nitrogenous  sub- 
stances, albumin,  etc.,  serves  in  the  formation  of  blood 
and  in  building  up  the  various  organs  of  the  body  ;  it 
is  called  the  plastic  food.  The  other,  consisting  of 
non-nitrogenous  substances,  the  fatty  bodies,  and  the 
so-called  carbohydrates,  resembles  ordinary  fuel,  serv- 
ing as  it  does  for  the  generation  of  heat ;  it  is  de- 
signated by  the  term  respiratory  food.  .  .  .  We 
heat  our  body,  exactly  as  we  heat  a  stove,  with  fuel 
which,  containing  the  same  elements  as  wood  and 
coal,  differs  essentially  from  the  latter  substance  in 
being  soluble  in  the  juices  of  the  body." 

In  order  to  establish  this  classification  of  foods,  he 


142  JUSTUS  VON   LIEBIG: 

pointed  out  that  the  food  of  all  animals  contains,  as 
we  have  seen,  besides  the  plastic  or  sanguigenous 
constituents  from  which  the  blood  and  the  organs  are 
derived,  a  certain  amount  of  the  substances  which  con- 
tain only  carbon,  hydrogen,  and  ox}^gen.  By  making 
various  mixtures  of  articles  of  food,  a  diet  can  be 
obtained  which,  so  far  as  its  composition  is  concerned, 
will  suit  the  needs  of  any  given  man  or  animal,  and  in 
making  such  mixtures  a  healthy  man  is  guided  by  an 
instinct  which  prescribes  for  him  the  best  proportions 
in  which  to  mix  the  plastic  and  non-nitrogenous 
materials  for  his  diet.  These  proportions  may  be 
altered  within  certain  limits,  which  again  vary  Avith 
the  individual,  his  mode  of  life,  state  of  health,  etc., 
and  may  even  be  varied  beyond  those  limits,  under 
compulsion,  without  at  once  involving  the  death 
of  the  individual;  but  such  alterations  are  never 
made  without  more  or  less  injury  to  the  bodily 
and  mental  powers  of  the  individual  concerned.  In 
no  case  can  life  be  for  long  maintained  if  the  pro- 
portion of  the  nitrogenous  constituents  be  reduced 
below  a  certain  fixed  minimum.  And  though,  on  the 
other  hand,  it  is  possible  to  maintain  life  on  a  purely 
albuminous  diet,  it  is  always  disadvantageous  to  do  so. 
Guided  by  what  was  then  known  of  the  composi- 
tion of  the  body  and  of  the  food-stuffs,  Liebig  con- 
cluded that  it  was  demonstrated  that  different  foods  are 
exceedingly  unequal  in  their  ability  to  influence  the  pro- 
ducing and  restoring  of  the  powers  which  enable  men 
and  animals  to  do  work  or  produce  manifestations  of 
energy  through  the  nervous  system :  that  wheat  sur- 
passes rye,  that  rye  surpasses  potatoes,  and  that  flesh 
/-  surpasses  all  other  foods  in  respect  to  the  production  of 
L.  these  effects.  Now,  the  proportion  of  the  plastic  to  the 

|><xx^*~e 

*+JSUU* 


HIS    LIFE    AND   WORK.  143 

non-nitrogenous  materials  (taking  Liebig's  data)  in 
the  case  of  potatoes  is  smaller  than  in  the  case 
of  rye,  that  in  the  case  of  rye  is  smaller  than 
that  in  the  case  of  wheat,  and  that  in  the  case  of 
wheat  again  is  very  much  smaller  than  that  in  beef 
or  mutton,  from  which  it  seemed  obvious  that  the 
plastic  constituents  of  food  must  be  the  proximate 
cause  of  the  power  to  do  work  and  of  the  ner- 
vous manifestations  in  the  animal  organism. "  This 
conclusion  is  confirmed  by  the  fact  that  all  the  effects 
which  animals  produce  by  their  brains  or  by  their 
muscles  are  determined  by  the  organised  structure 
of  their  bodies,  and  that  the  unorganised  parts,  such 
as  fats,  are  unable  to  change  their  relative  positions 
by  any  inherent  power  of  their  own. 

But  if  the  effects  producible  by  a  man  or  beast, 
whether  by  the  voluntary  or  involuntary  motions  of 
his  muscles  or  by  the  organs  of  sense,  depend  upon 
the  producing  and  restoring  of  the  organised  tissues, 
if  these  organised  tissues  are  built  up  and  renewed 
by  albuminoid  material  derived  from  the  blood,  and 
if  finally  the  albuminoids  of  the  blood  find  their  origin 
in  the  albuminoid  constituents  of  plants,  it  seems  to 
foUow  that  in  these  albuminoid  constituents  of  plants 
we  have  the  source  of  all  those  effects  which  animals 
produce  by  means  of  their  organs  of  sense,  thought, 
or  motion. 

Liebig  believed  that  in  this  relation  of  the  animal 
kingdom  to  the  vegetable  kingdom  he  had  found  a 
new  and  wonderful  revelation.  "  Plants,  which  serve 
as  food  to  animals,  are  the  producers  of  the  plastic 
constituents  of  food,  and  'hence  are  accumulators  of 
force."  * 

*  We  should  now  say  "  energy." 


144  JUSTUS   VON   LIEBIG: 

By  becoming  organised  parts  of  the  animal  body 
the  plastic  constituents  of  plants  determine,  ac- 
cording to  Liebig,  the  continuance  of  all  vital 
phenomena. 

But  what,  then,  is  the  function  of  the  non-nitro- 
genous food  ?  Liebig  found  in  this  the  source  of 
animal  heat. 

The  animal  body  is  not,  he  said,  merely  a  source 
of  mechanical  power  and  of  vital  actions ;  it  is  also  an 
apparatus  for  producing  heat ;  sufficient  heat  is  given 
off  in  a  year  by  an  adult  man  to  raise  about  twenty- 
three  thousand  pounds  of  water  from  freezing-point  to 
boiling-point.  This  heat  is  the  outcome  of  the  com- 
bination of  the  oxygen  of  the  air,  taken  up  in  respira- 
tion, with  the  constituents  of  the  food  in  the  body,  and 
the  amount  of  heat  produced  is  approximately  in 
proportion  to  the  oxygen  consumed.  On  comparing 
the  consumption  of  plastic  material  with  the  oxygen 
taken  up  by  the  lungs,  Liebig  found  that  the  com- 
bustible elements  of  the  former  were  insufficient  to 
convert  all  the  oxygen  absorbed  into  carbonic  acid 
gas  and  water — that  a  horse,  for  example,  takes  up 
about  five  times  as  much  oxygen  as  is  wanted  for  the 
complete  combustion  of  the  albuminoid  substances  in 
the  food.  For  this  and  other  reasons  he  concluded 
that  the  non-nitrogenous  substances  in  the  food 
supply  the  blood  with  materials  which  surpass  the 
albuminoid  compounds  in  their  tendency  to  undergo 
oxidation,  and  thus  protect,  as  it  were,  the  albuminoids 
from  the  destructive  action  of  the  oxygen.  This  is 
the  function,  according  to  Liebig,  of  the  non-nitrogen- 
ous part  of  food, 

"  Sugar,  starch,  and  fat,"  he  says,  "  serve  to  pro- 
tect the  organised  tissues ;  and,  in  consequence  of  the 


HIS    LIFE    AND    WORK.  145 

combination  of  their  elements  with  oxygen,  they  keep 
up  the  temperature  of  the  body." 

"  The  sulphurised  and  nitrogenous  constituents  of 
food  determine  the  continuance  of  the  manifestations 
of  force ;  the  non-nitrogenous  serve  to  produce  heat. 
The  former  are  the  builders  of  organs  and  organised 
structures  and  the  producers  of  force,  the  latter 
support  the  respiratory  process;  they  are  the 
materials  for  respiration." 

The  two  quotations  given  above  are  taken  from 
the  "Familiar  Letters"  (1851).  But  the  same  idea, 
very  clearly  expressed,  is  to  be  found  in  Part  I.  of 
his  second  "  Report  to  the  British  Association,"  pre- 
sented in  1842. 

This  beautiful  conception  quickly  won  its  way, 
and  for  a  long  time  it  was  generally  accepted.  It 
was,  in  a  word,  a  great  success;  but,  like  all  other 
classifications,  it  was  imperfect.  It  is  difficult  to  draw 
the  line  which  will  exactly  separate  the  plastic  foods 
from  those  which  only  support  respiration,  and 
physiology  now  teaches  us  that  all  varieties  of  food 
are  both  assimilable  and  respiratory.  But  the  value 
of  a  conception  of  this  kind  does  not  depend  on  its 
actual  and  final  truthfulness :  it  depends  on  its  use- 
fulness. A  theory,  as  Liebig  always  taught,  is  only 
a  tool.  It  is  only  valuable  if  we  can  employ  it  for 
the  purpose  of  extending  the  bounds  of  knowledge. 
Sooner  or  later  its  work,  like  that  of  other  tools,  will 
be  done,  and  it  will  be  cast  aside.  Liebig's  theory  of 
the  plastic  and  respiratory  foods,  though  now,  at 
last,  no  longer  serviceable,  in  its  day  did  yeoman's 
service.  Even  to-day  it  is  found  convenient  to  retain 
Liebig's  classification  of  foods  into  the  nitrogenous  and 
non-nitrogenous  groups ;  for  it  is  still  true,  and  always 
J 


146  JUSTUS   VON    LIEBIG: 

will  be,  that  the  members  of  the  two  groups  exhibit 
marked  differences  in  their  effect  on  the  animal 
organism.  The  nitrogenous  constituents  of  food 
alone  are  by  themselves  capable,  though  not  usually 
advantageously,  of  sustaining  animal  life.  They  alone 
contain  all  the  elements  that  are  required  both  for 
building  up  the  tissues  and  for  supporting  the  re- 
spiratory processes.  Trie  non-nitrogenous  consti- 
tuents, on  the  other  hand,  by  themselves  are  quite 
incapable  of  sustaining  life.  They  do  not  contain  the 
necessary  elements  for  forming  the  organised  tissues ; 
they  only  supply  those  elements  which  by  their  oxida- 
tion are  capable  of  serving  as  sources  of  heat  and 
work.  In  a  modified  form  this  is  the  distinction 
that  was  drawn  by  Liebig,  and  on  which  he  founded 
his  theory  that  the  use  of  the  non-nitrogenous  parts 
of  food  is  to  protect,  as  it  were,  the  nitrogenous 
constituents.  Before  Liebig,  although  physiologists 
had  experimented  with  various  simple  foods,  and  had 
learned  whether  this,  that,  and  the  other  substances 
were  suitable  for  the  use  of  animals,  their  results  had 
led  to  no  general  conclusions.  They  had  not  recog- 
nised, as  Liebig  did,  that  all  foods  fall  into  two  large 
and  fundamentally  distinct  classes.  It  was  this, 
perhaps,  which  led  Dr.  Theodor  von  Bischoff  to 
declare,  in  1874,  that  though  the  objections  which 
had  been  raised  on  physiological  grounds  against 
Liebig's  classification  were  undoubtedly  correct,  yet 
the  truth  of  his  views  as  a  whole  would  always 
remain,  and  that  it  was  impossible  to  deny  the  great 
merit  they  possess  of  pointing  out  in  the  briefest  way 
the  essential  differences  which  separate  the  several 
varieties  of  food. 

It  will  be  remembered  that  Liebig's  views  on  the 


HIS    LIFE    AND    WOKK.  147 

relations  of  plants  and  animals  led  him  to  declare  that 
through  their  nitrogenous  constituents  the  plants 
act  as  accumulators  of  energy.  This  brilliant  idea 
was  also  in  the  main  correct.  The  advance  of  know- 
ledge has  shown  us  that  plants  do  indeed  store  up 
energy — not,  however,  only  in  the  processes  by  which 
their  nitrogenous  parts  are  formed,  but,  speaking 
broadly,  by  their  life  processes  as  a  whole,  in  which, 
as  we  now  believe,  energy  derived  from  the  sun  is 
made  use  of  for  separating  the  carbon  and  oxygen 
from  the  carbonic  acid  gas  of  the  air.  This  energy 
remains,  stored  up  as  it  were,  in  the  new  substances 
formed  and  in  the  liberated  oxygen,  and  again  becomes 
available  on  the  recombination  of  the  carbon  and 
oxygen  either  in  our  bodies  or  under  other  conditions. 

Another  conclusion  of  Liebig's  which  led  to  a 
most  animated  discussion,  was  his  doctrine  of  the 
origin  and  functions  of  fat  in  the  bodies  of  animals. 

By  a  careful  investigation  of  the  conditions  under 
which  fat  appears  in  animals  he  was  led  to  conclude, 
positively,  that  fat  is  actually  elaborated  by  the 
organism ;  that  it  is  not  all  taken  in  as  fat  in  the 
food,  but  is  partly  produced  from  the  carbohydrates 
which  the  animal  finds  ready  prepared  for  him 
by  the  plants.  The  hypotheses  by  which  he 
sought  to  explain  this  phenomenon  are  no  longer 
acceptable,  but  the  fundamental  fact  of  the  pro- 
duction of  fat  by  animals  has  been  abundantly 
confirmed.  When  Liebig  first  announced  his  con- 
viction that  fat  is  produced  in  the  bodies  of 
animals  from  the  carbohydrates,  his  decision  was 
vigorously  criticised  by  some  of  the  leading  French 
chemists,  who  were  already  committed  to  the  oppo- 
site view.  About  a  year  before  Liebig's  Report  was 


148  JUSTUS   VON   LIEBIG  : 

published — viz.  on  August  20th,  1841 — Dumas  and 
Boussingault,  in  their  celebrated  lecture  on  the 
"  Statique  Chimique  des  Etres  Organises,"  had 
declared  that  plants  produce  fat,  and  that  animals 
consume  it ;  and  these  two  especially  threw  them- 
selves into  the  debate  on  this  subject,  which  soon 
became  lively,  and  was  not  quicky  concluded.  Liebig 
stated  that  the  food  consumed  by  the  herb-eating 
animals  does  not  contain  anything  like  as  much  fat 
as  that  which  they  store  up  in  their  bodies.  His 
opponents,  on  the  other  hand,  held  that  the  animals 
receive  all  their  fat  from  the  plants.  Curiously  enough, 
Liebig  was  shown  to  be  right,  largely  by  the  re- 
searches of  those  who  opposed  him. — This  sometimes 
happens  in  scientific  disputes,  and  had  already  occurred 
sufficiently  often  to  Liebig  to  lead  him  to  say  on  one 
occasion,  "  My  mill  has  ever  received  its  best  supply 
of  water  from  my  opponents." — Their  experiments 
showed,  indeed,  that  the  vegetable  food  of  animals 
contains  more  fat  than  had  previously  been  supposed, 
but  that  in  test  cases  the  amount  is  quite  insufficient 
to  account  for  the  quantities  that  are  deposited  in  the 
bodies  of  pigs  and  geese  when  they  are  given  a  vege- 
table diet.  The  question  was  finally  settled  when  it 
was  proved  that  bees  produce  wax,  which  Brodie  has 
shown  to  be  a  fat,  when  they  are  fed  exclusively  upon 
sugar. 

The  work  of  the  French  chemists  yielded,  how- 
ever, a  further  interesting  result.  It  showed  that  this 
producing  of  fat  from  the  carbohydrates  was  largely 
dependent  on  the  co-operation  of  nitrogenous  foods. 
This  Liebig  admitted,  and  also  that  under  certain 
conditions  the  nitrogenous  materials  themselves 
might  become  the  source  of  supplies  of  fatty  matter, 


HIS    LIFE    AND   WORK.  149 

At  a  later  stage  some  modern  physiologists  re- 
opened this  question,  and,  going  beyond  what  Liebig 
was  able  to  admit  concerning  the  producing  of  fat 
from  the  albuminoids,  assumed  that  all  the  fat 
produced  in  the  animal  comes  from  this  source. 
Liebig,  without  denying  that  this  view  might  be  right, 
held  that  all  that  could  be  said  with  certainty  was 
that  in  the  case  of  the  graminivora  the  albuminoids 
and  carbohydrates  work  together  to  produce  fat ; 
and  the  results  of  subsequent  experiments  have,  it 
may  fairly  be  said,  vindicated  his  opinion  on  this 
subject. 

So  much  has  been  said  about  the  classification  of 
foods  into  nitrogenous  and  non-nitrogenous,  that  it 
has  become  important  to  remind  the  reader  that 
neither  nitrogenous  food  alone,  nor  non-nitrogenous 
food  alone,  nor  both  together,  will  support  life. 
Organic  foods — that  is  to  say,  those  which  contain 
carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  and 
phosphorus — do  not  by  themselves  include  all  the 
materials  present  in  the  animal  body ;  and  it  is  said 
that  if  a  diet  composed  of  purely  organic  materials  be 
offered  day  after  day  to  an  animal,  he  will,  after  a 
time,  refuse  to  take  it — that  not  even  the  tortures 
of  starvation  will  induce  him  to  do  so. 

If  the  body  of  a  dead  animal,  or  a  portion  from 
almost  any  part  of  the  body  of  an  animal,  be  burnt  as 
completely  as  possible,  there  will  always  remain  a 
more  or  less  voluminous  residue  of  ash.  This  ash  or 
mineral  matter  is  as  essential  to  the  life  of  an  animal 
as  the  organic  matter,  and  it  must,  therefore,  be  pro- 
vided in  his  food.  At  one  time  the  importance  of 
mineral  matter  both  in  the  food  of  plants  and  animals 
was  to  a  great  extent  overlooked,  and  we  have  seen 


150  JUSTUS  VON   LIEBIG: 

that  even  comparatively  lately  it  was  supposed  that 
organisms  could  produce  mineral  matter  for  them- 
selves. The  importance  of  mineral  matter  for  the 
bones  of  the  higher  animals  was  of  course  recognised, 
but  that  was  all. 

Liebig,  as  has  been  seen  in  the  earlier  sections  of 
this  book,  was  pre-eminent  among  vegetable  physio- 
logists in  regard  to  the  importance  he  ascribed  to 
the  mineral  food  of  plants  ;  naturally,  therefore,  he 
did  not  overlook  its  vital  significance  in  the  animal 
economy.  When  we  have  said,  however,  that  mineral 
food  is  of  vital  importance  to  animals,  that  neverthe- 
less it  does  not  serve  as  .an  important  source  of  energy, 
and  have  added  a  few  facts,  such  as  that  the  bones 
contain  phosphate  of  calcium,  that  bile  contains  much 
sodium,  chiefly  in  combination  with  certain  peculiar 
acids,  we  have  told  almost  all  that  is  known.  In  fact, 
this  subject,  important  as  it  is,  is  still  imperfectly 
understood,  and  only  merits  this  brief  mention,  in 
order  that  the  preceding  pages  shall  not  mislead 
unscientific  readers  by  creating  the  idea  that  it  is 
only  the  organic  constituents  of  foods  which  are 
important. 

In  the  second  part  of  his  second  report  to  the  British 
Association  Liebig  attempted  to  trace  the  changes 
that  occur  during  the  processes  which  convert  the 
constituents  of  food  into  blood,  those  of  blood  into 
tissues,  and,  finally,  these  into  the  secretions  and 
excretions. 

The  value  and  interest  of  most  of  this  splendid 
review  of  physiology,  from  the  standpoint  of  the 
chemist,  has  now  necessarily  to  a  great  extent  passed 
away,  in  consequence  of  the  transformation  which  the 
subject  has  undergone  in  the  hands  of  a  host  of  modern 


HIS    LIFE   AND   WORK.  151 

workers.  Liebig  himself,  there  can  be  no  doubt,  fore- 
sa\v  that  to  a  great  extent  his  conclusions  in  this 
department  would  in  time  be  modified.  He  admitted 
frankly  that  some  of  his  results  had  surprised  him- 
self no  less  than  they  would  surprise  others ;  that  they 
had  excited  in  his  own  mind  the  same  doubts  which 
others  would  entertain;  that  he  gave  them  because 
he  was  convinced  that  the  method  by  which  they 
were  obtained  was  the  only  one  from  which  an  insight 
into  organic  processes  could  be  hoped  for.  He  felt 
that  they  deserved  attention  hi  so  far  as  they 
pointed  to  the  road  which  chemists  must  follow  if 
they  would  be  really  of  service  to  physiology  and 
pathology. 

By  showing  how  to  apply  chemistry  to  physiology, 
Liebig  insured,  first,  the  advance  of  physiology, 
and,  secondly,  the  overthrow  of  many  of  the  details 
of  his  own  contributions  to  its  advancement.  This 
second  effect  of  his  work  may  be  illustrated  by  an 
example  drawn  from  his  treatment  of  the  meta- 
morphoses of  the  tissues  alluded  to  above. 

The  basis  of  many  of  Liebig's  early  conceptions  con- 
cerning the  nature  of  the  tissues  was  the  supposed 
existence  of  the  substance  called  protein,  which  had 
been  obtained  by  the  physiologist  Mulder  from  albu- 
minoids by  the  action  of  caustic  potash.  When 
the  progress  of  physiological  investigation  showed, 
as  it  subsequently  did,  that  the  protein  of  Mulder  was, 
so  to  speak,  an  artificial  substance,  a  mere  product 
of  the  laboratory  and  no  true  component  of  the 
tissues  at  all,  all  those  hypotheses  of  Liebig's  which 
were  based  upon  the  protein  theory  fell  to  the  ground. 
But  the  very  fact  that  they  did  not  survive,  but  were 
overthrown  in  this  way  to  make  room  for  truer  con- 


152  JUSTUS  VON   LIEJBIC: 

eeptions,  was  itself  a  testimony  of  the  highest  kind  to 
the  immense  value  of  his  method,  since  the  very 
progress  which  led  to  the  overthrow  of  these  particular 
conclusions  was  itself,  in  no  small  degree,  the  outcome 
of  the  method  which  Liebig  had  given  to  physiology. 

It  is  worth  while  to  lay  emphasis  on  this  matter, 
for,  important  as  Liebig's  contributions  to  the  advance 
of  physiology  were,  they  are  to-day  to  a  great 
extent  forgotten.  This  was  the  case  even  twenty 
years  ago,  when  Theodor  von  Bischoff  said  on  the 
subject :  "  I  do  not  think  I  am  mistaken  if  I  hold  the 
opinion  that  there  are  not  many  among  the  younger 
physiologists  and  medical  men  who  know,  or  have 
even  a  distant  notion  how  great — or,  rather,  I  should 
say,  how  immense — the  influence  of  Liebig's  researches, 
writings,  and  teachings  has  been,  and  is  still,  not  only 
on  physiology  and  medicine,  but  on  organic  science 
at  large.  The  majority  enjoy  the  advantages  gained, 
and  rejoice  in  the  progress,  without  being  aware  of 
their  author.  They  consider  as  self-evident  the  facts 
established  by  Liebig  and  the  methods  and  principles 
of  research  diffused  by  his  teaching.  They  believe  it 
could  not  be  otherwise,  and  care  but  little  for  him  to 
whom  science,  and  with  science  they  themselves,  are 
indebted  for  their  present  position." 

The  man  Avho  wrote  these  words  was  not  only 
himself  an  eminent  biologist,  but  he  had  known  Liebig 
and  his  work  for  thirty  years.  He  was  one  who  knew 
the  condition  in  which  Liebig  found  physiology  and 
how  he  left  it.  On  the  whole,  it  seems  that 
what  Liebig  especially  did  for  physiology  was  this  : 
He  taught  the  physiologists  of  his  time  how  to 
frame  many  questions,  and  how  to  search  for  their 
answers. 


HIS    LIFE   AND    WORK.  153 

In  the  third  section  of  this  Report  Liebig  dealt 
with  the  phenomena  of  motion  in  the  animal  body. 
He  recognised  a  connection  between  the  oxygen 
absorbed  and  the  work  done,  and  he  perceived  that 
an  increased  transformation  of  muscular  fibre  deter- 
mines the  doing  of  a  greater  amount  of  work.  He 
perceived,  in  short,  an  intimate  relation  in  the 
animal  body  between  absorption  of  oxygen,  change 
of  matter,  and  manifestations  of  energy.  But  he  was 
too  earty  in  this  field,  and,  besides,  the  problem  was 
one  for  a  physicist  rather  than  for  a  chemist.  The 
thought  he  gave  to  the  subject  was,  however,  by  no 
means  unproductive.  In  connection  with  it  he  at- 
tacked a  question  of  the  greatest  practical  importance 
in  regard  to  the  feeding  of  animals  for  work — viz. 
whether  an  animal  when  at  work  requires  its  food 
to  be  enriched  with  the  nitrogenous  elements, 
or  whether  the  increased  demands  are  rather  upon 
the  non-nitrogenous  constituents.  The  answer  to 
this  question  for  some  time  seemed  doubtful,  but 
it  now  appears  to  be  pretty  clearly  proved  that, 
contrary  to  Liebig's  opinion,  under  ordinary  circum- 
stances the  enlarged  requirements  of  the  animal  are 
chiefly  for  the  non-nitrogenous  foods. 

The  final  solution  of  the  question  has  only  been 
arrived  at  by  following  a  line  of  investigation  sug- 
gested by  Liebig's  writings. 

Practically  speaking,  we  may  say  that  just  as  the 
carbon  of  the  food  is  ejected  from  the  animal  system 
through  the  lungs  in  the  form  of  carbonic  acid  gas 
after  its  work  is  done,  so  the  nitrogen  is  mainly — 
though  not,  indeed,  solely — ejected  by  the  higher 
animals  in  the  form  of  a  single  substance,  urea.  It 
follows  from  this  that  if  we  can  in  any  way  collect  day 


154  JUSTUS   VON   LIEBIG: 

by  day  the  urea  which  passes  from  an  animal  and 
weigh  it,  we  shall  have  an  approximate  measure  of 
the  amount  of  nitrogenous  tissue  used  up  during 
separate  periods.  Further,  if  we  divide  the  life  of  a 
given  animal  into  periods  of  work  and  periods  of 
rest,  and  compare  the  quantities  of  urea  thrown  oft 
during  those  periods  respectively,  we  shall  be  able 
to  tell  whether  increased  demands  have  been  made 
on  the  nitrogenous  matters  of  the  tissues  during 
the  working  periods ;  because  in  that  case  we  shall 
find  that  more  urea  is  produced  during  or  imme- 
diately after  work. 

In  order  to  trace  the  influence  of  work  on  the 
tissues  by  periodically  measuring  the  urea  produced 
it  is  necessary  to  devise  some  means  of  readily 
separating  the  urea  from  the  substances  which 
accompany  it,  and  then  to  measure  it.  This  was 
accomplished  by  Liebig  by  taking  advantage  of  the 
fact,  that  if  a  solution  of  corrosive  sublimate  be  added 
to  urea  in  solution,  these  two  combine  and  separate 
as  a  precipitate  of  definite  composition.  The  quantity 
of  the  urea  in  a  solution  may  be  determined  either 
by  collecting  and  weighing  the  precipitate — which  is 
troublesome — or,  more  simply,  as  Liebig  showed,  by 
adding  a  solution  of  corrosive  sublimate  of  known 
strength  to  the  solution  of  urea,  so  long  as  any  pre- 
cipitation occurs,  and  then  calculating  from  the 
amount  of  sublimate  employed  how  much  urea  was 
in  the  solution  to  be  tested. 

This  process,  though  superseded  of  late  years,  has 
been  of  immense  value,  not  only  to  the  student 
of  pure  science  in  the  study  of  the  transformations 
of  the  tissues  in  the  body,  but  also  in  the  hands  of 
physicians,  by  enabling  them  to  watch  the  action 


HIS    LIFE   AND   WORK.  155 

of  the  organ  (the  kidney)  by  means  of  which  urea 
is,  under  normal  conditions,  absorbed  from  the 
blood,  and  so  removed  from  the  system,  and  to 
detect  and  treat  certain  diseases.  Liebig  and  his 
pupils  also  enriched  physiology  by  a  chemical 
examination  of  blood,  by  a  study  of  the  nature  of 
bile,  and  by  comparative  work  on  the  elimination 
of  the  waste  products  of  man  and  the  carnivora. 
Jointly  with  Wohler  he  conducted  a  research  on 
uric  acid,  which  is  justly  regarded  as  a  model  of 
experimental  inquiry.  In  these  contributions  to 
science,  however,  though  Liebig  showed  his  wonder- 
ful powers  as  an  investigator,  he  was  not  touching 
any  of  the  fundamental  questions,  and  we  must  not, 
therefore,  dwell  upon  their  details,  but  pass  on  to 
his  inquiry  into  "the  motion  of  the  juices  in  the 
animal  body,"  *  in  which  he  suggested  some  further 
extensions  of  the  applications  of  chemical  and  physical 
laws  to  physiology. 

Nourishment  produced  from  the  food  is,  we  know, 
carried  to  every  part  of  the  body  by  the  blood.  It 
travels  through  tubes — some  of  them  large,  some 
of  them  very  small  indeed — which  extend  by  their 
ramifications  throughout  the  whole  organism.  But 
these  tubes  necessarily  have  walls,  though  some  of 
them  are  very  thin,  and  the  tissue  which  they  supply, 
however  well  it  may  be  provided  with  blood-vessels, 
cannot  all  of  it,  or  even  most  of  it,  be  in  actual 
contact  with  a  blood-vessel. 

The  question,  then,  is — How  does  the  nourishment 
find  its  way  from  the  blood,  through  the  walls  of  the 
vessels  and  cells,  to  the  points  where  it  is  wanted  ? 
And,  again,  how  do  the  products  of  the  never-ceasing 

*  "  Chemistry  of  Food,"  by  Dr.  Gregory,  published  1848. 


156  JUSTUS   VON   LIEBIG  : 

changes  that  go  on  in  the  tissues  find  their  way 
through  the  same  obstacles  and  into  the  blood 
which  is  to  carry  them  away  when  their  work  is 
done  ? 

If  we  take  a  bag,  or  closed  tube  made  of  parchment, 
of  bladder  or  of  any  similar  membrane,  and  put  in  it 
alcohol  or  a  solution  of  common  salt,  and  if  we  then  put 
the  closed  end  of  this  under  distilled  water  in  a  basin, 
we  shall  soon  find  that  the  water  in  the  outer  vessel  is 
no  longer  pure.  It  will  contain  alcohol,  or  salt,  as  the 
case  may  be  ;  for  these  things,  and  many  others,  when 
dissolved,  have  the  power  of  passing  through  such 
membranes.  The  name  osmose  has  been  given  to  the 
process  by  which  this  transference  of  solids  in  solution 
through  membranes  takes  place;  and  it  has  been 
supposed  that  nourishment  is  conveyed  to  the  living 
tissues  by  a  process  of  this  kind. 

From  the  results  of  a  number  of  experiments,  some 
made  by  himself,  others  by  other  investigators,  Liebig 
formed  the  opinion,  that  in  the  organism  the  causes 
which  determine  the  motions  of  the  juices  are  far 
more  powerful  than  that  to  which  the  name  osmose 
has  been  given.  That  the  passage  of  the  digested 
food  into  the  blood,  the  passage  of  the  nutrient  fluid 
outwards  from  the  blood,  and  its  motion  towards  the 
parts  where  its  constituents  acquire  vitality,  involve 
something  more  than  a  simple  law  of  mixture.  He 
concluded  that  the  membranes  probably  exert  an 
important  influence  on  the  secretions.  The  following 
quotation  will  perhaps  indicate  the  position  he  took 
as  well  as  a  more  detailed  account  of  his  work : — 

"  Since,"  he  says,  "  the  chemical  nature  and  the 
mechanical  character  of  membranes  and  skins  exert 
the  greatest  influence  on  the  distribution  of  the  fluids 


HIS    LIFE    AND    WORK.  157 

in  the  animal  body,  the  relations  of  each  membrane 
presenting  any  peculiarity  of  structure,  or  of  the 
different  glands  and  systems  of  vessels,  deserve  to  be 
investigated  by  careful  experiment ;  and  it  might 
very  likely  be  found  that  in  the  secretion  of  the  milk, 
the  bile,  the  urine,  the  sweat,  etc.,  the  membranes  and 
cell-walls  play  a  far  more  important  part  than  we  are 
inclined  to  ascribe  to  them ;  that,  besides  their 
physical  properties,  they  possess  certain  chemical 
properties  by  which  they  are  enabled  to  produce 
decompositions  and  combinations,  true  analyses;  and 
if  this  were  ascertained,  the  influence  of  chemical 
agents,  of  remedies,  and  of  poisons  on  those  properties 
would  be  at  once  explained." 

It  is  nearly  fifty  years  since  these  words  were 
written,  and  the  subject  is  still,  owing  to  its  difficulty, 
not  far  from  where  Liebig  left  it,  except  that  the 
modern  physiologist  would  remind  us  that  osmose  in 
a  living  membrane  is  probably  very  different  from 
that  in  a  dead  membrane.  But  is  not  this  just 
what  Liebig  intended  to  point  out  when  he  suggested 
that  the  membranes  and  cell-walls  play  a  specially 
important  part  in  the  phenomena  in  question  ? 
Sooner  or  later  Liebig's  suggestions  will  probably 
bear  fruit,  and,  indeed,  an  interesting  step  in  the 
direction  indicated  by  the  above  remarks  has  been 
made  by  Professor  Waymouth  Reid  within  the  last 
few  years.  Professor  Reid,  by  means  of  experiments 
with  a  frog's  skin,  has  found  that  in  the  living 
membrane  there  is  a  distinct  absorptive  force  which 
makes  osmose  take  place  more  readily  from  without 
inwards  than  in  the  reverse  direction. 

A  year  before  the  publication  of  this  account  of 
his  experiments  on  osmose  Liebig  produced,  in  his 


158  JUSTUS   VON    LIEBIG: 

researches  on  the  chemistry  of  food,  an  account  of  his 
investigation  of  the  constituents  of  flesh. 

The  introductory  part  of  this  little  book  illustrates 
rather  forcibly  Liebig's  power  of  giving  "  hard  knocks." 
In  his  own  work  he  had  often  shown  the  good  use 
that  may  be  made  of  an  exact  knowledge  of  the  chemi- 
cal composition  of  substances.  But  he  now  found  it 
necessary  to  remind  the  physiologists  that  the  function 
of  chemistry  in  regard  to  physiology  is  by  no  means 
exhausted  when  a  substance  is  analysed  and  neatly 
labelled  with  a  formula  more  or  less  correct,  especially 
as  the  most  exact  analyses  cannot  by  themselves 
always  lead  us  to  true  formulae. 

It  seems  that  the  discovery  of  a  close  similarity 
in  composition  between  casein,  albumin,  and  fibrin, 
from  animal  and  vegetable  sources,  which  appeared 
to  throw  much  light  on  the  processes  of  digestion 
and  nutrition,  had,  in  Liebig's  opinion,  created  an 
undue  sense  of  the  importance  of  the  mere  chemical 
composition  of  organic  substances,  with  the  result,  as 
he  said,  that  for  some  time  a  great  many  analyses  had 
been  made,  but  not  much  real  progress.  This  led 
him  to  give  a  new  example,  drawn  from  one  of  his 
own  most  brilliant  investigations,  of  the  true  manner 
in  which  organic  chemistry  should  be  applied  to  the 
investigation  of  physiological  problems. 

There  are  two  reasons  why  the  mere  analyses  of 
the  substances  which  occur  in  animal  bodies  cannot 
by  themselves  considerably  advance  physiology.  First, 
that  an  organic  analysis  is,  as  he  reminded  his 
readers,  a  means  of  acquiring  knowledge,  but  is  not 
that  knowledge  itself.  The  results  of  an  analysis, 
however  perfect  it  may  be,  do  not  give  the  least 
information  as  to  the  arrangement  of  the  elements 


HIS    LIFE    AND    WORK.  159 

in  the  molecules  of  the  substances,  nor  as  to  how 
they  will  behave  themselves  under  the  influence 
of  chemical  agencies ;  and  till  we  know  this 
we  cannot  possibly  form  any  definite  views  of  the 
part  a  given  compound  will  play  in  the  vital  pro- 
cesses. 

Secondly,  it  is  only  when  the  number  of  atoms  in 
the  molecules  of  a  compound  is  small  that  an  analysis 
can  be  trusted  even  to  lead  to  a  correct  formula  ;  and 
as  the  molecules  of  the  substances  dealt  with  in 
physiological  chemistry  often  are  large,  small  in- 
evitable errors  in  their  analyses  may,  and  do,  lead  to 
very  serious  misconceptions. 

There  is,  however,  a  method,  which  was  well 
known  to  a  master  like  Liebig,  by  which  we  can 
both  check  the  result  of  an  analysis  and  simul- 
taneously gain  some  knowledge  of  the  arrangement 
of  the  atoms  in  the  molecules  of  an  organic  substance. 
This  method  is  simple  enough  in  principle.  It  may 
be  described  as  an  application  of  the  maxim  "  divide 
to  conquer."  It  consists  in  this,  that  when  the  com- 
position of  a  substance  has  been  found  as  accurately 
as  is  possible  by  analysis,  and  its  most  probable 
formula  has  been  provisionally  fixed  upon,  portions  of 
it  are  treated  with  reagents,  so  that,  if  possible,  its 
molecules  shall  be  broken  up  into  two  or  more 
substances  with  less  complex  molecules.  These  more 
simple  compounds  are  then  in  their  turn  submitted  to 
analysis,  and  the  results  so  arrived  at  are  compared 
with  those  given  by  the  substance  from  which  they 
were  derived. 

For  each  organic  substance  there  may  be  several 
formulae  which  agree  almost  equally  well  with  the 
results  of  its  analysis,  but  probably  only  one  of 


1 60  JUSTUS   VON   LIEBIG  : 

these  will  also  agree  with  the  formula  deduced 
from  the  results  of  the  analyses  of  the  substances 
derived  from  it. 

The  importance  of  this  method  of  control  had  not, 
it  is  true,  been  entirely  overlooked  by  workers  in  the 
field  of  physiology;  but  it  is  subject  to  sources  of 
error,  which  had  not  been  properly  guarded  against. 
In  order  that  this  method  shall  guide  the  investigator 
to  true  results,  the  decomposition  products  must 
every  one  of  them  be  fully  and  thoroughly  investi- 
gated. If  one  of  them  be  missed,  for  example,  an 
error  results  which  may  mislead  the  investigator  and 
his  followers,  with  most  deplorable  results. 

Above  all,  hypothetical  compounds  must  not  be 
assumed  to  exist  among  the  products  oi  the  decom- 
position in  order  to  support  preconceived  ideas,  or  to 
save  trouble. 

These  are  words  which  might  well  be  written  in 
letters  of  gold  over  the  door  of  every  laboratory  for 
chemical  research,  and  Liebig,  by  insisting  on  the 
importance  of  the  principle  thus  laid  down,  did  a 
distinct  service  to  the  sciences  which  it  was  ever  his 
object  to  advance. 

In  the  second  section  of  the  book  Liebig  dealt 
with  his  discovery  of  the  formula  of  creatine,  and 
with  his  other  important  discoveries  concerning  the 
components  of  flesh.  His  method  in  this  work 
afforded  to  the  chemist  and  physiologist  an  admirable 
illustration  of  the  principles  laid  down  in  the  preceding 
paragraphs;  but  the  subject  is  of  too  technical  a 
character  to  be  generally  interesting  in  spite  of  the 
important  results  he  obtained. 

In  the  last  section  of  his  "Chemistry  of  Food" 
Liebig  dealt  with  the  chemistry  of  cookery,  so  far  as 


HIS   LIFE   AND   WORK.  161 

concerns  the  use  of  flesh.  It  is  obvious,  he  pointed  out, 
that  if  the  flesh  employed  for  food  is  to  become  again 
flesh  in  the  animal  body,  none  of  the  constituents  of 
raw  flesh  ought  to  be  withdrawn  from  it  in  its  pre- 
paration for  the  table.  If  any  essential  constituent  be 
removed  from  a  piece  of  flesh,  that  piece  of  flesh  will 
no  longer  have  the  power  of  resuming  in  the  body  the 
form  and  quality  on  which  its  properties  in  a  living 
organism  depend.  But  when  flesh  is  boiled  in  water, 
more  or  less  of  its  saline  constituents  are  removed, 
together  with  a  certain  amount  of  its  organic  con- 
stituents. It  follows  that  boiled  meat  eaten  without 
the  liquor  in  which  it  was  boiled  is  less  well  adapted 
for  nourishing  an  animal,  in  proportion  to  the  amount 
of  matter  that  has  been  extracted  from  it — in  pro- 
portion, that  is  to  say,  to  the  length  of  time  during 
which  the  process  of  boiling  is  continued  and  to  the 
quantity  of  water  employed. 

It  is  possible  to  extract  from  finely  divided  meat, 
by  the  action  of  cold  water,  a  great  deal  of  albumin- 
ous matter — the  proportion  varies  with  the  age  of  the 
animal  and  other  circumstances — hence  it  is  not  wise 
to  steep  fresh  meat  for  long  in  cold  or  warm  water. 
On  the  other  hand,  washed  muscular  fibre  becomes 
hardened  by  boiling  it  in  water,  consequently  the 
tenderness  of  boiled  meat  depends  largely  upon  the 
cook's  success  in  depositing  the  soluble  albuminous 
matter  coagulated  among  the  fibres,  since  this 
prevents  to  some  extent  the  contracting  or  hardening 
mentioned  above.  The  method  to  be  recommended, 
therefore,  for  boiling  meat,  especially  when  the  water 
in  which  it  is  boiled  will  not  be  consumed,  is  to 
plunge  the  cold  meat  into  boiling  water,  then  after  a 
few  minutes  to  cool  the  water  to  from  76  degrees  to 
K 


162  JUSTUS   VON   LIEBIG: 

72  degrees,*  and  to  maintain  this  temperature  for 
a  sufficient  time. 

It  is  easy  to  understand  that  the  effect  of  the 
brief  immersion  in  boiling  water  is  to  form  an 
outer  case  of  hardened  flesh,  which  protects  the 
mass  beneath  from  the  solvent  action  of  the  water 
afterwards.  Then  the  long  -  continued  moderate 
heating  gradually  warms  the  whole  to  a  sufficient 
temperature  to  coagulate  the  albumin  in  the  juice 
of  the  meat  without  unduly  hardening  it.  The 
colour  of  underdone  meat,  as  Liebig  explained,  is 
due  to  the  mass  having  been  insufficiently  heated. 
The  albumin  of  meat  juice  congeals  at  about  60°  C.,t 
but  the  colouring  matter  of  the  blood  requires  a 
higher  temperature.  That  is  why  the  meat  should 
be  heated  to  at  least  72  degrees.  Finally,  a  rather  lower 
temperature  may  be  employed  for  white  meat,  such 
as  the  flesh  of  fowls,  as  this  contains  little  blood. 
This  last  fact  explains  why  such  meat  is  more  quickly 
cooked  than  beef  and  mutton. 

The  superior  flavour  of  roast  meat,  as  will  now 
be  seen,  is  largely  due  to  the  fact  that  in  cooking 
it  nothing  has  been  washed  out  of  it;  besides  this, 
the  retained  albumin  reduces  hardening  of  the  fibres 
to  the  utmost  possible  extent.  But  even  in  roasting, 
the  escape  of  the  juices  should  be  retarded  by  heating 
as  strongly  as  possible  at  first ;  the  juice  then  hardens 
on  the  outside  and  produces  a  protecting  surface, 
which  prevents  subsequent  loss. 

In  order  to  prepare  soup  we  must,  as  far  as 
possible,  reverse  all  the  above  proceedings,  and  con- 
duct the  operations  so  as  to  extract  as  much  as 

*   165  to  158  degrees  Fahr. 
f  140  degrees  Fahr. 


HIS    LIFE   AND  WORK.  163 

possible  from  the  meat.  For  this  purpose,  therefore, 
Liebig  advised  that  the  meat  should  be  very  finely 
divided,  and  then  be  brought  into  cold  water  and 
heated  very  gradually  to  the  boiling-point,  at  which 
it  should  be  kept  for  a  few  minutes. 

Soup  made  in  this  way  may  not  form  a  jelly  on 
cooling,  but  it  will  be  very  rich  in  the  most  valuable 
of  the  soluble  parts  of  meat.  Housewives  have  always, 
and  probably  do  still,  attach  great  importance  to  the 
tendency  of  soup  to  form  a  jelly.  Liebig  insisted 
that  the  importance  of  this  quality  is  much  over- 
rated. 

As  the  high  temperature  Liebig  employed  at  the 
end  of  his  process  may  coagulate  albumin,  a  modifica- 
tion of  it  has  been  suggested  in  which  the  finely 
divided  meat  is  placed  in  cold  water  and  then  gradu- 
ally heated  as  before,  but  not  to  so  high  a  tempera- 
ture. Thus  we  avoid  coagulating  the  albuminous 
substances  dissolved  at  the  lower  temperature,  which 
are  consequently  retained  in  solution. 

A  few  words  must  now  be  said  about  Liebig's 
celebrated  extract  of  meat. 

By  boiling  down  extract  of  lean  flesh,  made  by 
Liebig's  process,  at  a  low  temperature  in  a  water-bath, 
or  by  one  of  the  other  methods  of  low-temperature 
evaporation  which  are  at  the  command  of  chemists,  we 
obtain  "  Liebig's  extract  of  meat."  In  1847  Liebig 
did  not  lay  so  much  stress  on  the  usefulness  of  this 
product  as  he  did  afterwards.  In  fact,  at  that  time 
he  only  recommended  it  as  capable  of  making  strong, 
well-flavoured  soup,  and  as  likely  to  prove  a  valuable 
restorative  to  wounded  soldiers. 

In  his  celebrated  "Familiar  Letters  on  Chemistry" 
Liebig  again  dealt  with  this  subject,  and  recommended 


164  JUSTUS   VON   LIEBIG: 

soup  in  the  strongest  terms  as  the  medicine  of  the 
convalescent.  He  here  pointed  out  that  in  South 
America,  in  Mexico,  and  in  Australia,  where  animals  are 
chiefly  valuable  for  their  skins  and  wool,  there  might 
be  made  from  meat  of  only  nominal  value  *  immense 
quantities  of  the  best  extract,  which  might  acquire 
great  importance  for  potato-eating  populations,  and 
replace  soup  in  the  hospitals.  In  these  letters 
he  also  discussed  more  fully  the  question  of  the 
dietetic  value  of  gelatine,  and  of  soups  containing 
it,  quoting  the  report  of  a  commission  of  the  French 
Academy,  with  Magendie  at  its  head,  to  show  that 
the  value  of  a  soup  is  very  little  increased  by  the 
addition  to  it  of  gelatine,  since  numerous  experiments 
have  proved  that  by  itself  gelatine  has  little  or  no 
dietetic  value — at  any  rate,  that  it  cannot  be  made  to 
act  as  a  substitute  for  a  true  plastic  food,  in  spite 
of  the  nitrogen  which  it  contains. 

The  extraordinary  and  rapid  rise  into  popularity 
of  the  condensed  extract  of  meat  was  remarkable, 
and  it  was  made  more  wonderful  by  the  fact  that 
for  a  long  time  a  most  marked  want  of  agreement 
existed  as  to  its  real  value.  Whilst  some  people 
regarded  it  as  highly  unwholesome,  or,  indeed,  almost 
a  poison,  owing  to  the  large  proportion  of  potash  salts 
in  it,  others — some  of  them,  however,  from  interested 
motives,  it  is  to  be  feared — went  so  far  as  to  recom- 
mend it  as  a  really  sufficient-  substitute  for  meat ; 
and,  more  wonderful  still,  a  great  many  others 
believed  them.  These  last,  however,  were,  perhaps, 
to  be  excused.  Ignorant  of  the  most  elementary 

*  Lean  beef  in  Australia  about  this  time  was  worth  from  one 
halfpenny  the  pound  to  nothing ;  great  quantities  were  thrown 
away  after  boiling  down  for  the  fat. 


HIS    LIFE    AND    WORK.  165 

principles  of  science  as  the  general  population  was 
then,  -and  still  is,  and  familiar  as  they  were  with 
the  striking,  and  to  them  quite  unintelligible,  results 
that  often  follow  the  administering  of  apparently  trivial 
quantities  of  active  chemicals,  such  as  quinine  or 
arsenic,  it  is  not,  after  all,  really  surprising  that  many 
people  were  ready  to  believe  almost  anything  they 
were  told  about  this  wonderful  invention  of  the  great 
German  chemist. 

Liebig  himself  was  not  likely  to  be,  and  never  was, 
under  any  mistake  about  the  value  of  extract  of  meat. 
At  first  it  would  appear  from  his  chemistry  of  food 
that  he  regarded  it  as  a  valuable  restorative,  and  as 
a  substitute  for  soup.  Afterwards  he  perceived  that 
it  might  have  a  wider  application,  and  become  the 
means  of  bringing  to  Europe  some  part  of  all  the  food 
that  was  wasting  at  a  distance  literally  for  the  want 
of  anyone  to  eat  it.  But  he  meant  the  extract  to 
be  eaten  with  liberal  additions  of  bread,  peas,  lentils — 
with  food,  that  is,  which  contains  a  good  supply  of  those 
nitrogenised  constituents  in  which  the  meat  extract 
was,  from  the  process  of  its  manufacture,  intentionally 
and  of  necessity  wanting.  It  is  still  difficult  to  under- 
stand its  exact  action ;  but  the  tendency  is  to  regard 
it  as  a  useful  stimulant,  ranking,  perhaps,  with  tea 
and  coffee,  but,  of  course,  with  its  own  peculiar 
virtues.  Bischoff  has  pointed  out  that  the  salts  in 
extract  of  meat  are  probably  just  those  which  are 
most  wanted  for  the  producing  of  flesh,  though,  of 
course,  salt  must  be  added ;  but  as  nitrogenous  matters 
of  vegetable  origin  are  inferior,  for  the  food  of  car- 
nivora,  to  those  obtained  by  means  of  flesh,  he  con- 
cluded that  a  diet  in  which  the  vegetable  albuminoids 
replace  those  of  flesh  must  be  inferior  to  flesh  food, 


166  JUSTUS   VON   LIEBIG: 

even  when  supplemented  by  meat  extract.  Liebig, 
however,  as  Bisehoff  has  said,  by  no  means  overlooked 
this,  and  never  recommended  the  extract  as  equiva- 
lent to  flesh,  but  only  as  a  substitute  for  it  when 
taken  with  suitable  accompaniments. 

In  concluding  his  contribution  to  domestic  chemis- 
try— so  far  as  the  treatment  of  flesh  is  concerned — 
Liebig  turned  to  the  processes  of  salting  and  preserving 
meat.  By  collecting  the  brine  from  a  given  piece  of 
flesh  which  had  been  pickled,  and  measuring  it,  he 
found  that  it  corresponded  to  about  a  third  of  the 
juice  of  the  given  flesh;  and  on  subjecting  this  brine 
to  analysis  Liebig  was  interested  to  discover  that  it 
contained  the  constituents  of  soup,  which  had  been 
extracted  to  a  greater  extent  than  can  be  done  in  the 
ordinary  way,  even  by  boiling  water.  Not  only  the 
salts,  but  a  large  quantity  of  albumin,  together  with 
creatinine,  etc.,  were  found  in  it.  These  striking  obser- 
vations were  of  the  greatest  practical  interest.  They 
explained  why  salt  meat  affords  a  less  valuable  food 
than  the  same  meat  unsalted ;  why,  in  the  days 
when  salt  meat  had  to  be  largely  employed  for  food 
during  the  winter,  our  countrymen,  in  spite  of  the 
other  conditions  of  their  lives  being  in  many  ways 
favourable,  were  scourged  by  various  diseases  from 
which  we  ourselves  are  comparatively  free ;  and  why, 
even  in  modern  times,  toilers  on  the  sea,  when  they 
are  driven  to  subsist  for  a  long  while  on  salt  meat, 
often  suffer  for  it  severely.  In  the  course  of  his 
experiments  on  salting  meat  Liebig  made  the  further 
interesting  observation '  that  the  presence  in  the  salt 
of  calcium  or  magnesium  compounds,  in  some 
degree  protects  flesh  from  its  extractive  power. 
It  seems  as  though  the  salts  of  these  metals,  on 


HIS    LIFE    AND    WORK.  167 

meeting  with  the  soluble  phosphates  of  the  flesh, 
produce  insoluble  substances  by  interacting  with 
them,  viz.  phosphate  of  calcium,  or  of  magnesium, 
which  cannot  be  so  freely  removed  from  the  flesh 
as  the  more  soluble  alkaline  phosphates  themselves ; 
and  he  suggested  that  meat  pickled  with  salt 
containing  these  metals  would,  if  eaten  with  a 
sufficiency  of  the  esculent  vegetables,  which  are  rich 
in  potash,  offer  a  very  superior  diet  to  ordinary  salted 
meat. 

One  of  the  most  interesting  problems  connected 
with  physiology  is  the  question  whether  the  life 
processes  of  living  organisms  are  determined  by  the 
action  of  a  so-called  "  vital  force." 

It  is  not  possible, when  we  think  upon  the  wonderful 
results  that  flowed  from  Liebig's  endeavours  to  apply 
the  methods  of  organic  chemistry  to  physiology,  to 
avoid  asking  ourselves  the  question — Did  he,  then, 
consider  that  in  the  laws  of  chemistry  and  physics  we 
have  a  key  which  may  ultimately  unlock  the  chamber 
which  hides  the  mystery  of  the  origin  of  life  ?  Did 
he  suppose  that  the  laws  of  chemistry  and  physics 
were  the  sole  laws  of  physiology  ?  We  know  that  he, 
like  Davy  and  some  others,  rejected  altogether  the 
idea  that  there  exists  a  peculiar  vital  force  which  is 
able  to  override  the  laws  of  chemistry — as,  for  example, 
by  the  creation  of  mineral  substances  from  the  inor- 
ganic components  of  their  food — and  which  presides 
unassisted  over  the  phenomena  exhibited  by  organised 
beings.  But  did  he  go  so  far  as  to  reject  the 
very  idea  of  the  existence  of  any  vital  force,  as 
some  thinkers  have  been  inclined  to  do  ?  It  would 
be  easy  to  find  passages  in  his  writings  which  seem 
to  imply  that  this  was  the  case.  "It  is  evident,"  he 


168  JUSTUS  VON  LIEBIG: 

says  in  Chapter  XX.  of  his  Familiar  Letters,*  "  that 
physiology  has  two  foundations,  and  that  by  the  fusion 
of  physiological  physics,  the  foundation  of  which  is 
anatomy,  with  physiological  chemistry,  which  rests  on 
animal  chemistry,  a  new  science  must  arise,  a  true 
physiology,  which  will  stand  in  the  same  relation  to 
the  physiology  of  the  present  day  as  modern  chemistry 
does  to  that  of  the  eighteenth  century." 

Then,  after  showing  how  chemistry  had  in  the  past 
absorbed  and  made  part  of  itself  branches  of  physics, 
with  the  result  that  the  latter  had  determined  the  whole 
character  of  modern  chemistry,  he  goes  on  to  say  that — 
"  Exactly  in  the  same  way  the  more  accurate  know- 
ledge of  vital  phenomena  will  establish  the  conviction 
that  a  number  of  physiological  properties  depend  on 
chemical  composition ;  and  physiology,  when  it  shall 
have  taken  up  animal  chemistry  as  a  part  of  itself, 
will  possess  the  means  of  investigating  this  relation  of 
dependence.  It  will  then  be  able  to  find  a  juster 
expression  for  physiological  phenomena." 

But  elsewhere  he  makes  it  plain  that  by  such 
expressions  as  these  he  did  not  by  any  means  mean 
to  imply  that  in  chemistry  and  physics  we  have  the 
whole  foundation  of  physiology.  Thus  later  on  he 
writes : — 

"  It  is  certain  that  a  number  of  effects  observed  in 
the  living  body  are  determined  by  chemico-physical 
causes,  but  it  is  going  much  too  far  to  conclude  from 
this  that  all  the  forces  which  act  in  the  organism  are 
identical  with  those  which  govern  dead  matter  .... 
Those  who  adopt  such  an  opinion  have  lost  sight  of  the 
first  and  simplest  rule  of  physico-chemical  inquiry, 
which  directs  us  to  prove  that  an  effect  which  we  ascribe 

*  Third  edition. 


HIS    LIFE    AND    WORK.  169 

to  a  cause  is  really  due  to  that  cause,  and  no  other." 
And  he  closes  this  chapter,  after  showing  how  little  we 
know  even  of  the  known  forces  and  their  relations, 
by  saying  that  this  imperfect  state  of  knowledge  of 
the  essence  and  effects  of  known  natural  forces 
"  explains  how  it  comes  to  pass  that  at  this  moment 
we  are  unable  to  solve  the  question  in  reference  to 
the  existence  of  a  peculiar  force  or  influence  acting  in 
the  living  organism,  by  the  method  of  exclusion  or 
elimination." 

Bischoff,who  was  Liebig's  intimate  friend  and  corre- 
spondent, has  shown  us  by  what  he  has  said  on  this 
subject  that  Liebig  himself  did  not  deny  that  there 
may  be  a  distinct  vital  force  which  determines  the 
production  of  organised  structures,  and  works  in  them 
with  the  chemical  and  physical  forces.  Vital  force  for 
Liebig  was  most  nearly  like  chemical  force  and  related 
to  organised  structures,  somewhat  as  chemical  force 
is  related  to  chemical  compounds. 

The  tendency  of  physiologists  and  pathologists,  for 
a  long  period  before  Liebig  joined  in  their  work,  had 
been  to  attempt  to  investigate  the  most  complex 
phenomena  of  life  before  they  were  acquainted  with 
the  simplest.  In  his  efforts  to  apply  organic  chemistry 
to  physiology  Liebig  threw  himself  with  characteristic 
enthusiasm  into  the  company  of  those  who  were  be- 
ginning to  realise  the  inevitable  sterility  of  such  a 
method.  It  was,  as  has  been  said,  his  object  and 
theirs  to  introduce  into  physiology  the  method  which- 
in  a  few  years  had  revolutionised  some  branches 
of  chemistry — the  method,  that  is  to  say,  of  pro- 
ceeding from  the  simple  to  the  complex.  It  seemed 
to  him  that  chemistry  and  physiology  had  reached 
such  a  stage  that  a  fusion  at  the  boundaries  of  these 


170  JUSTUS  VON  LIEBIG: 

two  sciences  might  be  looked  forward  to  as  one  of 
the  most  striking  results  of  scientific  progress  that 
would  be  attained  in  the  future.  Physiology,  he 
thought,  could  no  longer  dispense  with  chemistry  in 
the  study  of  vital  phenomena,  and  chemistry  was 
prepared — largely  by.  Liebig's  own  work,  it  must  be 
added — to  enter  into  the  service  of  physiology. 

These,  then,  were  his  objects  as  a  student  of 
physiology — to  make  the  methods  of  physics  and 
chemistry  the  methods  of  this  subject  also,  and  to 
bring  about  a  union  of  chemistry  and  physiology  that 
should  result  in  a  new  and  a  greater  physiology,  which 
should  embrace  these  two  great  branches  of  knowledge 
which  had  been  too  long  separated. 

The  measure  of  his  success  can  be  best  expressed 
by  quoting  the  following  extract  from  the  writings  of 
Bischoff,  who  knew  Liebig,  and  who  knew  physiology 
both  before  Liebig  set  his  hand  to  his  self-imposed 
task  and  after  his  labours  were  over.  Nearly  at  the 
end  of  his  address  on  the  influence  of  Liebig  on  the 
development  of  physiology,  he  said :  "  However  great 
and  immortal  may  be  the  services  of  Aristotle,  Galen, 
Vesalius,  Harvey,  Linmeus,  Haller,  Cuvier,  Charles 
Bell,  J.  Miiller,  and  others  to  physiology ;  however 
greatly  they  and  others  may  have  enriched  our  know- 
ledge in  the  province  of  organic  nature,  I  can  find  no 
proof  in  the  history  of  science  that  any  single  one  of 
these  has  so  influenced  and  altered  the  views  arid 
methods  of  physiology,  and  also  consequently  of 
medicine,  by  facts  and  methods  as  Liebig.  I  regard 
Liebig  as  the  one  who  has  brought  organic  natural 
science  into  the  pathway  of  exact  investigation." 

And  now  let  us  return  for  a  moment  to  Liebig's 
great  generalisations  on  the  relations  of  plants  and 


HIS    LIFE    AND    WORK.  171 

animals  to  each  other  and  to  mother  earth.  It  will 
not  be  necessary  to  dwell  for  long  on  this  topic,  for 
most  readers  by  this  time  will  have  discovered  for 
themselves  the  main  features  of  the  wonderful  cycle 
of  changes  which  Liebig's  mind  first  made  plain  to  us. 
They  have  learnt  from  him  how  plants  absorb  from 
the  air  and  from  the  earth  simple  inorganic  substances 
— carbonic  acid  gas,  water,  and  ammonia,  with  a  few 
mineral  salts  ;  how  by  the  help  of  sunlight  these  are 
so  altered  that  the  oxygen  of  the  carbonic  acid  gas  is 
returned  in  the  elemental  state  to  the  air,  whilst  the 
rest  are  retained,  and  go  to  form  first  the  various 
parts  of  vegetables,  afterwards  the  blood,  the  flesh,  the 
bones,  and  the  nerves  of  animals ;  and  how,  either 
in  the  bodies  of  the  herb-eating  animals,  or  in  those 
of  the  flesh-eaters,  the  carbon  in  the  course  of  time 
again  enters  into  combination  with  oxygen,  which  the 
animals  absorb  from  the  air  by  their  lungs,  and  is 
returned  to  the  air,  except  so  far  as  concerns  that 
portion  which  is  retained  in  their  tissues  by  young 
growing  animals.  How  in  the  same  way  the  nitrogen 
of  ammonia,  or  of  nitrates,  and  the  mineral  matters  are 
also  thrown  off,  at  a  rate  approximately  equal  to  that 
of  their  consumption,  and  returned,  the  salts  to  the 
earth,  the  ammonia  to  the  air  or  earth ;  and  how 
finally,  on  the  death  of  the  animal,  every  trace  of  its 
components  return  by  the  processes  of  decay  to 
their  original  condition  of  lifeless  inorganic  matter, 
ready  to  nourish  new  generations  of  plants  and 
animals,  provided  only  that  man  does  not — as,  alas,  he 
too  often  does — disturb  the  balance  of  nature  by 
casting  into  the  sea  that  which  should  be  used  for  the 
enrichment  of  the  land. 

Looking  at  the  matter  from  another  point  of  view, 


172  JUSTUS  VON   LIEBIG: 

we  have  seen,  with  Liebig's  aid,  how  the  plants  are, 
as  he  expressed  it,  "  the  accumulators  of  force ; " 
how  these,  utilising  some  of  the  energy,  as  we  now 
call  it,  which  reaches  them  from  the  sun,  reduce  car- 
bonic acid  gas,  so  that  its  carbon  enters  presently 
the  bodies  of  animals  in  such  forms  that  it  can  after- 
wards liberate,  on  its  re-union  with  the  oxygen,  sup- 
plies of  energy  which  are  available  for  doing  work 
in  its  various  forms,  or  for  maintaining  the  necessary 
temperature  of  the  organism.  In  short,  if  we  have  not 
learned  from  Liebig  quite  all  that  science  can  teach 
us  to-day  on  this  subject,  it  is  no  fault  of  Liebig's, 
but  due  to  the  fact  that  the  "  Physicists "  were  not 
quite  ready  for  the  chemists  when  Liebig  attacked  this 
question. 


HIS    LIFE   AND   WORK.  173 


CHAPTER  VIII. 

EDUCATIONAL  AND   OTHER  WORK. 

Influence  on  the  Methods  of  Education— Giessen  Laboratory — 
Liebig  as  a  Teacher— Founding  of  other  Chemical  Schools — 
His  Attempts  to  carry  results  of  his  Studies  to  those  outside 
the  Universities — Interest  in  Technical  Education — What  is 
Technical  Education — Supposed  "Spontaneous  Combustibility" 
of  Human  Bodies— Literary  Work. 

IT  might  reasonably  be  supposed  by  anyone  who  had 
become  acquainted  for  the  first  time  with  so  much  of 
Liebig's  work  in  science  as  it  has  been  possible  to 
allude  to  in  the  foregoing  pages,  that  surely  this  must 
be  the  sum  of  it.  That  he  must  have  spent  his  days 
and  nights  in  his  laboratory  and  his  study ;  that  as  a 
teacher  he  must  have  been  content  to  deliver  his 
university  lectures,  and  have  devoted  all  the  time 
not  occupied  by  them  to  meditating,  experimenting, 
and  writing.  But  this  was  by  no  means  the  case. 
Liebig  made  a  great  departure  in  the  teaching  of 
chemistry.  And  we  may  even  venture  to  call  him 
the  earliest  of  "  extension  teachers,"  since  he  had  the 
happy  idea  of  conveying  to  the  general  public  some 
notion  of  the  progress  of  his  science  in  his  university 
and  elsewhere,  by  means  of  a  series  of  letters  which 
he  addressed  to  the  Augsbwrger  Allgemcinc  Zeituny. 
In  these  letters  he  gave,  from  time  to  time,  the 
results  of  such  of  his  inquiries  as  he  could  render 
intelligible  to  general  readers. 

A  very  prince  of  extension  teachers,  surely  !     Can 


174  JUSTUS   VON   LIEBIG: 

it  be  doubted  that  these  wonderful  letters — "  Liebig's 
Familiar  Letters  on  Chemistry " — had  much  to  do 
with  the  present  intelligent  attitude  of  the  German 
"  practical  man  "  to  science,  which  has  contrasted  so 
strangely  with  that  of  his  average  English  brother  for 
many  years  past,  much  to  the  material  disadvantage 
of  the  latter,  it  is  to  be  feared. 

We  have  already  learnt  that  on  his  return  to 
Germany  from  Paris  Liebig  obtained,  through  the 
interest  of  Humboldt,  an  appointment  first  as  extra- 
ordinary, and  soon  afterwards  as  ordinary,  professor  of 
chemistry  in  the  little  German  University  of  Giessen. 
Here  he  stayed  for  twenty- eight  years.  Speaking  of 
his  life  there,  he  said  afterwards,  "It  was  as  if 
Providence  had  led  me  to  the  little  university.  At  a 
larger  university,  or  in  a  larger  town,  my  energies 
would  have  been  divided  and  dissipated,  and  it  would 
have  been  much  more  difficult,  and  perhaps  im- 
possible, to  reach  the  goal  at  which  I  aimed ;  but  at 
Giessen  everything  was  concentrated  in  work,  and  in 
this  I  took  passionate  pleasure." 

A  few  years  before  Liebig  went  to  Giessen,  it 
was,  as  he  has  told  us,  "  a  very  wretched  time  for 
chemistry  in  Germany."  Only  the  pharmacists  had 
preserved  any  remains  of  practical  instruction,  and  in 
order  to  get  any  real  training  it  was  necessary  for 
Germans  to  go  to  Paris  or  to  Stockholm.  Even  in 
those  places  the  student  found  no  public  laboratories, 
but  had  to  rely  on  such  interest  as  he  could  command 
to  gain  admission  to  the  workroom  of  some  chemist 
of  distinction,  which,  after  all,  was  sometimes  only 
a  garret  or  a  cellar.  Liebig,  as  we  have  seen,  be- 
came the  pupil  and  friend  of  Gay-Lussac,  and  in 
his  laboratory  formed  the  idea  of  effecting  a  reform 


HIS    LIFE   AND   WORK.  175 

at  home.  Soon  after  receiving  his  appointment,  he 
took  his  first  step  by  opening  his  first — or,  rather,  the 
first — public  laboratory  for  the  teaching  of  practical 
chemistry  in  Germany.  Pupils  soon  began  to  stream 
in,  so  that  the  teaching  of  analysis  and  other  parts 
of  practical  chemistry  had  to  be  organised  on  a 
systematic  plan.  This  necessity  led  to  the  intro- 
duction of  a  system  of  teaching  elementary  and 
advanced  practical  chemistry  on  which  all  his  suc- 
cessors have  founded  their  methods. 

Actual  teaching  in  the  ordinary  sense  in  practical 
work  was  only  given  in  the  Giessen  laboratory  to  be- 
ginners ;  this  work  was  put  into  the  hands  of  skilful 
assistants.  Liebig  himself  took  charge  of  the  special 
pupils ;  their  progress  largely  depended  on  themselves. 
Their  master  gave  the  task,  and  supervised  the  doing 
of  it.  There  was  no  actual  instruction.  Liebig  received 
every  morning  from  each  pupil  a  report  upon  what  he 
had  done  on  the  previous  day,  as  well  as  his  views 
upon  the  work.  He  approved  or  criticised  this,  but 
every  student  was  obliged  to  follow  his  own  course. 
Owing  to  constant  intercourse  each  student  partici- 
pated in  the  work  of  all  the  others ;  every  one  was  a 
learner,  every  one  was  a  teacher.  Twice  a  week  Liebig 
gave  a  review  of  the  most  important  questions  of  the 
day — a  report  of  his  own  work,  combined  with  that  of 
the  students  and  with  the  researches  of  other  chemists. 

Work  went  on  from  daybreak  till  nightfall.  There 
was  no  amusement  and  no  dissipation  to  be  had  in 
Giessen,  and  the  only  complaint,  which  was  a  frequent 
one,  was  that  of  Aubel  (the  laboratory  man),  who 
could  not  get  the  workers  to  depart  in  the  evening, 
when  he  wanted  to  clean  the  laboratory. 

In  his  practical  teaching   Liebig  laid  great  stress 


176  JUSTUS  VON   LIEBIG: 

on  the  producing  of  chemical  preparations — on  the 
students  preparing,  that  is  to  say,  pure  substances  in 
good  quantity  from  crude  materials.  The  importance 
of  this  was,  even  in  Liebig's  time,  often  overlooked, 
and  it  was,  he  tells  us,  more  common  to  find  a  man 
who  could  make  a  good  analysis  than  to  find  one 
who  could  produce  a  pure  preparation  in  the  most 
judicious  way.  There  is  no  better  way  of  making 
oneself  acquainted  with  the  properties  of  a  substance 
than  by  first  producing  it  from  the  raw  material,  then 
converting  it  into  its  compounds,  and  so  becoming 
acquainted  with  them.  By  the  study  of  ordinary 
analysis  one  does  not  learn  how  to  use  the  important 
methods  of  crystallisation,  fractional  distillation,  nor 
acquire  any  considerable  experience  in  the  proper 
use  of  solvents.  In  short,  one  does  not,  as  Liebig 
said,  become  a  chemist. 

Unfortunately,  owing  to  the  readiness  with  which 
analysis  lends  itself  to  competitive  examinations,  the 
importance  of  this  side  of  experimental  chemistry  has 
for  many  years  been  greatly  exaggerated  by  many 
English  teachers.  There  are  signs,  however,  that 
sounder  views  are  now  reasserting  themselves  in  the 
minds  of  teachers. 

It  was  during  the  early  }^ears  at  Giessen  that 
Liebig  busied  himself  with  the  task  of  improving 
the  methods  of  organic  analysis ;  and  in  a  few  years, 
when  this  work  was  completed,  the  Giessen  laboratory 
must  have  presented  a  busy  scene.  Talented  young 
men  were  now  streaming  in,  not  only  from  Ger- 
many, but  from  all  parts  of  Europe  and  from  the 
United  States  of  America ;  and  Liebig  had  working 
under  his  supervision  a  band  of  twenty  or  more  skilful 
and  indefatigable  young  chemists,  by  whom  thousands 


HIS    LIFE   AND   WORK. 

of  experiments  and  analyses  were  carried  out  every 
year.  From  their  results  the  master  gained  an 
abundance  of  the  facts  and  materials  out  of  which  he 
developed  the  wonderful  conceptions  with  which  he 
enriched  chemistry,  physiology,  and  agriculture. 

Liebig's  system  of  teaching  the  methods  of  re- 
search to  advanced  students  gives  a  "  character "  to 
scientific  education  in  Germany  to  this  day.  Students, 
when  they  come  back  from  Germany,  tell  us  that  in 
German  universities  the  lectures  and  elementary 
practical  instruction  are,  if  anything,  inferior,  cer- 
tainly not  superior,  to  the  teaching  in  our  own  schools 
and  universities,  and  that  the  well-taught  Englishman 
when  he  goes  to  a  German  university  is  certainly  not 
at  a  disadvantage  in  this  respect.  What  he  finds 
there,  and  what  it  is  difficult  to  find  at  home,  in  spite 
of  the  great  and  valuable  contributions  of  our  country- 
men to  science,  is  an  opportunity  for  soaking  himself 
with  the  spirit  and  methods  of  research  by  joining 
a  numerous  band  of  young  and  devoted  workers, 
with  whom  he  will  be  in  constant  intercourse  from 
eight  in  the  morning  to  six  at  night,  hearing  and 
seeing  nothing  for  a  year  or  two  but  original  experi- 
ments all  conducted  under  the  guidance  of  a  master 
mind. 

All  this,  the  preliminary  courses,  on  which  we 
at  home  may  pride  ourselves,  the  great  centres  of 
organised  scientific  investigation  which  are  the  glory 
of  Germany,  we  owe  to  the  early  labours  of  Liebig 
in  his  little  laboratory  at  Giessen !  Through  his 
work  the  Giessen  University  became  one  of  the 
forces  of  the  world. 

When  we  remember  that  a  very  few  years  be- 
fore Liebig  went  to  Giessen  he  could  not  find  in 


178  JUSTUS  VON   LIEBIG  : 

all  Germany  any  one  who  could  teach  him 
chemistry,  and  that,  as  a  lad,  he  had  followed  a 
professor  from  Bonn  to  Erlangen,  in  order  that 
the  professor  might  carry  out  a  promise  to  analyse 
some  minerals  with  him,  only  to  find  that,  unfortu- 
nately, his  guide  did  not  himself  know  how  to  do  it, 
we  can  hardly  sufficiently  admire  the  energy  and 
insight  which,  in  a  few  short  years,  enabled  Liebig  to 
build  up  a  complete  system  of  public  instruction, 
which  in  ite  main  features  still  seems  to  us  to  come 
very  near  to  being  a  council  of  perfection. 

In  this,  the  first — one  might  almost  say,  the  ideal 
— school  of  chemistry,  Liebig  gathered  round  him  the 
elite  of  the  ambitious  and  able  young  students  in  this 
science  from  the  whole  civilised  world,  so  that  an 
immense  number  of  the  chemists  of  to-day  owe  their 
education,  either  directly  or  indirectly,  to  him.  From 
England  students  flocked  to  him,  so  that  English 
chemistry  especially  came  under  his  influence,  the 
more  so  that  Hofmann,  his  brilliant  pupil,  afterwards 
directed  the  first  chemical  laboratory  opened  in  Eng- 
land for  giving  public  instruction  in  the  science. 

This  is  not  the  place  for  introducing  a  long  list 
of  the  names  of  Liebig's  eminent  pupils.  Such  a  list 
would  only  be  interesting  to  a  limited  number  of 
readers.  It  will  be  sufficient,  therefore,  to  say  that 
Liebig's  English  pupils  have  shown  his  influence  not 
only  by  their  work  in  pure  chemistry,  as  teachers  and 
as  investigators,  but  that  they  will  be  found  equally 
eminent  among  the  ranks  of  those  who  have  devoted 
themselves  to  the  applications  of  chemistry  in  the 
various  departments  of  industry. 

Liebig  as  a  lecturer  was  not,  it  seems,  exactly 
eloquent,  but  his  personality  was  magnetic,  and  he 


HIS   LIFE   AND    WORK.  179 

could  say  what  he  wanted.  He  had  a  greater  gift 
than  eloquence.  He  could  stimulate  the  reflective 
powers  of  his  pupils  and  make  them  think.  This 
was  the  secret  of  his  success  and  theirs. 

Hofmann  says  of  him  that  "  whoever  has  had  the 
good  fortune  of  attending  his  lectures,  will  not  easily 
forget  the  deep  impression  of  his  peculiar  style  of 
eloquence.  Liebig,"  he  says,  "  was  not  exactly  a  fluent 
speaker,  but  there  was  an  earnestness,  an  enthusiasm 
in  all  he  said,  which  irresistibly  carried  away  the 
hearer.  Nor  was  it  so  much  the  actual  knowledge  he 
imparted  which  produced  this  effect  as  the  wonderful 
manner  in  which  he  called  forth  the  reflective  powers 
of  even  the  least  gifted  of  his  pupils.  And  what  a 
boon  it  was,  after  having  been  stifled  by  an  oppressive 
load  of  facts,  to  drink  the  pure  breath  of  science,  such 
as  flowed  from  Liebig's  lips.  What  a  delight,  after 
having  perhaps  received  from  others  a  sackful  of 
dry  leaves,  suddenly,  in  Liebig's  lectures,  to  see  the 
living,  growing  tree." 

It  was  not,  however,  really  in  lecturing  that  Liebig 
excelled,  but  in  the  laboratory.  Here  he  was  followed 
not  only  because  he  was  admired,  but  because  he 
was  loved  still  more.  His  pupils  felt  a  pleasure  in 
submitting  themselves  to  his  fascinating  control. 
And  Hofmann  tells  us  that  if  anything  could 
exceed  their  wonder  at  the  amount  of  work  he  did 
himself  with  his  own  hands,  it  was  the  wonder  they 
felt  at  the  mountain  of  toil  which  he  got  them  to  go 
through  themselves ;  that,  if  anything  exceeded  their 
pride  in  his  friendship  and  approval,  it  was  their 
delight  to  know  that  they  helped  him,  and  that 
whilst  they  were  receiving  his  lessons  they  Avere  also 
performing  his  work.  The  aid  that  he  obtained  in 


180  JUSTUS   VON   LIEBIG: 

this  way  was  doubtless  considerable,  but  he  never 
failed  to  give  full  credit  for  such  aid,  and,  indeed,  so 
far  was  he  from  underrating  it,  that  in  his  generosity 
he  often  gave  a  pupil  the  whole  credit  for  a  success 
obtained  by  experiments  suggested  by  himself  and 
based  upon  his  own  previous  trials  and  discoveries. 

In  his  autobiographical  fragment,  from  which  I 
have  made  so  many  extracts,  Liebig,  when  speaking 
of  the  wonderful  chapter  of  accidents  by  which  he 
made  the  acquaintance  of  Gay-Lussac,  says  that  "since 
he  found  favour  as  a  boy  in  the  sight  of  Thenard, 
Humboldt,  Dulong,  and  Gay-Lussac,  it  had  frequently 
been  his  experience  that  marked  talent  awakens  in  all 
men,"  he  believes  without  exception,  "  an  irrepressible 
desire  to  bring  about  its  development."  Whether  he 
goes  too  far  in  saying  this  or  not,  there  can  be  no 
doubt  that  in  Liebig's  own  character  this  instinct 
existed  in  a  most  marked  degree. 

The  founding  of  Liebig's  School  of  Chemistry  at 
Giessen  formed  an  epoch  in  the  history  both  of 
science  and  of  education.  Almost  from  the  day  when 
this  school  was  inaugurated,  chemistry  and  the 
branches  of  science  connected  with  chemistry  have 
advanced  by  leaps  and  bounds.  It  is  impossible  not 
to  find  one  of  the  most  potent  causes  of  this  advance 
in  the  work  that  was  done  at  Giessen  by  Liebig.  The 
great  success  of  this  laboratory  quickly  led  to  the 
building  of  others,  and  soon  every  university  at  least 
possessed  such  a  laboratory.  At  first  they  were  modest 
places  enough,  many  ot  them,  till  Hofmann  on  his 
recall  from  England  to  Germany  was  provided  with 
something  very  like  a  palace  at  Bonn.  It  is  custom- 
ary, in  Germany,  to  provide  the  professor  with  a 
residence  in  the  laboratory,  and  so  fine  were  the  apart- 


HIS    LIFE    AND   WORK.  181 

ments  provided  at  Bonn  that  the  King  of  Prussia, 
when  he  opened  the  building,  is  said  to  have  re- 
marked :  "  I  should  like  to  live  here  myself."  Soon 
afterwards  a  second  palatial  building,  also  for  Hof- 
mann,  was  built  at  Berlin,  and  thus  an  era  of  palatial 
laboratories  was  inaugurated.  Other  countries,  in- 
cluding England,  followed  suit  more  or  less  quickly, 
and  now,  as  we  ah1  know,  not  only  the  universities,  but 
all  our  chief  towns,  are  provided,  some  with  one,  and 
some  with  more  than  one,  laboratory,  which,  though 
not  aLvays — nor,  indeed,  often — a  palace,  is  efficient 
and  fully  equipped  for  teaching  and  frequently  for 
chemical  research.  Indeed,  few  towns  of  even  the 
second  and  third  rank  are  now  quite  without  some 
provision  for  the  practical  study  of  the  subject, 
whilst  our  leading  schools  have  also,  in  the  great 
majority  of  cases,  provided  themselves  with  similar 
equipment.  Much  doubtless  still  remains  to  be  done, 
but  the  progress  made  is  already  very  great,  and  it 
may  all  be  traced  to  the  inspiration  of  Liebig. 

And  what  is  the  result  ?  Will  the  work  done  in 
these  lecture-rooms  and  laboratories  be  worth  their 
cost  ?  In  seeking  to  answer  this  question,  we  must  not 
forget  that  the  value  of  these  places  of  public  instruc- 
tion in  chemistry  does  not  consist  simply  in  the  fact 
that  they  provide  a  certain  number  of  workshops, 
more  or  less  magnificent,  more  or  less  well  provided, 
for  the  use  of  those  who  desire  to  study  pure 
chemistry.  They  provide  also  practical  instruction 
for  that  much  larger  and  equally  important  class 
who  purpose  to  devote  their  lives  to  the  service  of 
their  fellows  in  medicine,  in  the  various  and  ever- 
growing chemical  industries,  and  in  a  variety  of  other 
directions  too  numerous  to  mention.  And,  again,  we 


182  JUSTUS   VON   LIEBIG 

must  remember  that  chemical  laboratories  did  not  for 
long  stand  alone ;  presently  other  such  work-places, 
physical  laboratories,  biological  laboratories,  engineer- 
ing laboratories,  rose  beside  them,  ready  to  do  for 
physics,  biology,  and  engineering  what  the  chemi- 
cal laboratories  were  doing  for  chemistry.  The 
result,  neglecting  altogether  the  immediate  material 
gains,  which  though  difficult  to  calculate  must  be 
enormous,  is  briefly  this — that  civilised  mankind  is 
rapidly  learning  the  importance  of  facts  and  the  value 
of  the  experimental  method  by  which  facts  are  gained, 
and  is  realising  better  than  for  many  centuries  the 
dignity  and  the  intellectual  value  of  intelligently- 
directed  handwork. 

So  long  as  the  recognised  method  of  solving  every 
problem  was  to  sit  down  and  think  about  it,  it  was 
not  unnatural  that  those  who  worked  with  their  hands 
should  be  looked  upon  as  necessarily  inferior  to  the 
head-workers.  But  the  influences  developed  during 
the  last  fifty  years  are  steadily  changing  the  whole 
aspect  of  affairs,  and  it  cannot  but  be  that  before  long 
the  intelligent  hand-worker  in  every  department  will 
receive  a  fuller  measure  of  esteem  than  has  ever 
before,  as  far  as  we  know,  been  awarded  to  him. 

One  of  the  most  beautiful  and  fascinating  experi- 
ments of  the  chemist  is  to  prepare  a  very  clear, 
strong,  hot  solution  of  a  salt  more  soluble  in  hot  than 
in  cold  water,  and,  after  protecting  this  from  the 
approach  of  dust,  to  let  it  stand  till  cool.  If  the  ex- 
periment be  perfectly  made,  such  a  solution  will  re- 
main a  solution — it  maybe  indefinitely,  at  any  rate  for 
a  long  while  ;  no  crystals  of  the  solid  will  make  their 
appearance,  though  there  is  far  more  of  it  in  the 
liquid  than  the  water  present  can  normally  retain  in 


HLS    LIFE    AND  ^VOHK.  183 

the  liquid  state.  But  if  the  most  tiny,  invisible  frag- 
ment of  the  solid  salt  be  allowed  to  touch  the  solution 
at  any  point,  a  change  will  at  once  set  in,  crystals  will 
appear  at  that  point,  will  quickly  become  visible,  and 
will  spread  with  ever-increasing  rapidity,  till  in  a  few 
minutes  or — maybe,  in  a  few  moments — what  was 
before  fluid  will  become  a  solid  mass,  as  if  by  magic. 

It  was  somewhat  in  this  sense  that  the  founding 
of  Liebig's  laboratory  at  Giessen  was  the  cause  of 
the  movement  which  is  now  rapidly  introducing 
what  is  sometimes  called  the  scientific  method  in  so 
many  spheres  of  human  activity.  All  the  necessary 
elements  for  the  change  existed  before  Liebig  went 
to  Giessen.  His  fruitful  idea  acted  like  the  crystal. 
It  provided  the  necessary  nucleus. 

I  have  already  spoken  of  Liebig  as  a  very  early 
exponent  of  the  idea  which  is  at  the  bottom  of  the 
"  University  Extension  Movement."  He  endeavoured 
to  bring  the  learning  accumulated  in  the  university 
to  the  people  at  large  in  two  ways — first,  by  his 
celebrated  letters  on  chemistry ;  secondly,  by  bringing 
to  the  university  selected  persons  from  the  provinces 
to  attend  his  courses  of  lectures,  in  order  that  on 
returning  they  might  carry  a  little  knowledge  and 
some  interest  back  with  them  into  the  provinces, 
and,  maybe,  sow  the  seeds  which  should  produce 
greater  things  afterwards.  This  he  made  possible 
by  inducing  the  Government,  after  his  call  to  Munich 
in  1852,  to  grant  stipends  to  a  number  of  school- 
masters from  different  districts  to  enable  them  to 
defray  the  expenses  of  the  visit  to  the  city.  He 
hoped  in  this  way  to  point  out  the  road  to  mental 
culture  to  those  who  had  the  task  of  educating  the 
country  populations. 


184  JUSTUS   VON    LIEBIG: 

Speaking  of  the  results  of  this  experiment,  in 
1861,  he  said  in  the  course  of  an  academical  address : 
"It  must  be  confessed  that  even  among  those  who 
have  not  had  the  chance  of  attending  our  gymnasia,  or 
our  modern  and  technical  schools,  the  opinion  is  rooted 
that  a  little  more  knowledge  is  of  use  even  to  the 
most  common  hand- worker ;  that  some  knowledge  of 
botany  to  the  gardener,  some  knowledge  of  chemistry 
to  the  soap-boiler,  the  tanner,  or  the  dyer,  is  essential 
to  the  carrying  on  of  their  businesses  ;  that  a  gar- 
dener is  not  a  worse  gardener  for  knowing  a  little 
of  plant  life;  that  a  baker,  because  he  knows  what 
bread,  meal,  and  salt  are;  or  a  soap-maker,  because 
he  truly  knows  the  nature  of  fat,  ashes,  and  lye, 
what  are  their  good  qualities,  and  how  they  may 
be  recognised  by  tests — that  these  workmen  will 
not  be  any  the  worse  makers  of  bread  or  soap 
because  they  know  this.  Even  the  most  simple 
citizen  thinks  it  a  gain  if  his  neighbour,  who 
may  be  a  magistrate,  has  some  knowledge  of 
the  principles  on  which  the  rules  of  health  are 
established."  Then,  after  discussing  some  defects  in 
the  German  agricultural  colleges  as  they  then  were, 
he  went  on  to  say :  "  The  agriculturist  and  techno- 
logist must  learn  that  he  lives  in  a  cruel  time,  when 
existence  becomes  more  difficult  every  day  for  the 
incompetent  and  weak,  and  will  soon  perhaps  be  im- 
possible." His  remarks  on  this  occasion  are  said  to 
have  given  great  offence.  Fortunately  for  Germany, 
however,  the  lesson  was  by  no  means  altogether 
thrown  away,  in  spite  of  the  opposition  it  aroused. 

As  has  already  been  explained,  Liebig's  famous 
"Familiar  Letters  on  Chemistry"  were  originally  a 
series  of  letters  published  in  an  important  South 


HIS    LIFE    AND    WORK.  185 

German  newspaper.  They  were  afterwards  collected, 
and  on  the  occasion  of  preparing  a  third  edition  in 
1851,  Liebig  took  the  opportunity  of  adding  a  number 
of  letters  on  the  origin  and  development  of  chemistry. 

The  first  letter  in  this  edition  is  especially  inter- 
esting; in  it  Liebig  lays  down,  with  the  greatest  clear- 
ness, the  practical  relations  of  the  sciences  to  one 
another,  and  that  of  the  sciences  to  the  arts  with 
which  they  are  respectively  connected,  and  indicates 
the  manner  in  which  each  of  these  must  approach 
another  for  help  and  guidance ;  he  shows  the  con- 
ditions which  must  be  fulfilled,  for  example,  before 
chemistry  can  help  to  solve  the  problems  of  physio- 
logy or  contribute  to  the  development  of  a  chemical 
industry. 

In  many  respects  chemistry  is,  as  he  here  points  out, 
like  mathematics.  The  latter  teaches  us  in  its  applica- 
tion how  to  measure  land,  to  erect  buildings,  to  raise 
weights.  In  short,  it  is  an  instrument  which  confers 
the  most  obvious  advantages  on  those  who  know  how 
to  employ  it.  On  the  other  hand,  mathematics,  by 
means  of  a  language  of  its  own,  teaches  us  how  to 
draw  logical  conclusions  according  to  definite  rules, 
and  to  express  them,  in  a  simple  manner.  We  all  know 
that  mechanicians,  physicists,  and  astronomers  use 
mathematics ;  that  it  is  an  indispensable  instrument 
for  the  ends  they  strive  to  reach.  In  order  to  make 
use  of  mathematics,  they  must  become  so  expert 
in  the  subject  that  its  management  almost  becomes 
a  mechanical  habit.  But  notwithstanding  the  value 
of  this  instrument,  it  is  not  the  mere  instrument  which 
does  the  work.  Besides  having  the  necessary  fami- 
liarity with  the  processes  of  mathematics,  the  mechani- 
cian or  astronomer  must  be  able  to  propound  questions 


186  JUSTUS  VON   LIEBIG- 

to  himself,  and  to  test  the  truth  of  the  answers  given 
by  mathematics.  It  is  only  if  he  has  these  further 
powers  that  he  is  qualified  to  undertake  to  inves- 
tigate nature.  Mathematics,  the  instrument,  can  only 
help  astronomy,  physics,  and  mechanics  when  it  is  in 
the  hands  of  some  one  who  can,  so  to  speak,  propound 
problems  for  it  to  be  used  upon.  Besides  a  mastery 
of  mathematics,  the  astronomer,  the  physicist,  and 
the  mechanician  must  possess  acute  observing  power 
and  imagination.  These  two  last  afford,  so  to  say,  the 
motive  power.  Of  course  the  mathematics  are  equally 
essential,  but  they  are  not  a  cause,  they  are  an  instru- 
ment ;  mathematical  work,  as  we  know,  may  actually 
be  to  some  extent  done  by  machines,  and  we  must 
not  confuse  the  instrument  with  the  cause  in  this 
case,  just  as  we  must  not  ascribe  to  a  steam-engine 
results  which  have  really  been  brought  about  by  the 
human  intellect. 

And  so  it  is  with  chemistry  and  the  experimental 
sciences.  These  also — putting  aside  their  value  as  a 
mental  training,  and  in  other  ways  which  do  not 
concern  us  at  present — these  also  are  instruments  ;  and 
discoveries  in  chemistry,  in  physics,  and  so  on,  like 
discoveries  in  mathematics,  are  simply  steps  towards 
the  perfecting  of  the  instrument.  Chemistry  and  the 
other  sciences,  like  mathematics,  each  of  them  speaks 
a  language  of  its  own;  and  if  we  would  apply  any 
one  of  them  to  the  service  of  man  in  this  or  that 
department,  we  must  be  thoroughly  acquainted  with 
that  language.  But  here  again,  as  in  mathematics, 
these  physical  sciences  do  not  make  discoveries  for 
us.  If  we  apply  chemistry  to  a  chemical  problem 
set  out  in  the  right  way,  chemistry  will  find  us  the 
answer  to  that  problem,  provided,  of  course,  that  we 


HIS    LIFE    AND    WORK.  187 

do  not  go  beyond  the  powers  of  the  instrument  for  the 
time  being.  But  the  question  must  be  clearly  and 
definitely  put.  If  the  ideas  of  the  inquirer  are  not 
clear  as  to  the  problem  to  be  solved,  chemistry  can 
give  him  no  help.  The  inquirer,  in  short,  must 
understand  the  instrument  as  a  whole ;  it  is  not 
enough  that  he  shall  have  seen  a  wheel  here  and  a 
wheel  there ;  he  must  also  have  sagacity  and  observing 
power  ;  he  must  be  able  to  propound  definite  questions, 
and  understand  how  to  test  the  truth  of  the  answers 
obtained  by  yet  other  questions  when  that  is 
necessary. 

"  Can  men,"  asked  Liebig,  "  who  do  not  apprehend 
the  nature  of  scientific  investigation  in  a  philosophical 
spirit,  and  who  cannot  interpret  the  language  of 
phenomena — can  such  men  be  expected  to  derive  the 
least  advantage  from  the  discoveries  of  chemistry  or 
physiology ;  and  can  they  be  deemed  capable  of 
making  the  most  insignificant  application  of  those 
discoveries  to  practical  purposes  ? " 

These  were  the  considerations  which  led  Liebig  to 
take  great  interest  in  technical  education  ;  which  led 
him  to  praise  the  apothecary,  who,  after  learning  the 
elements  of  his  art  in  the  shop,  resorted  to  the 
university  for  instruction  in  the  science  on  which  it 
rests;  and  to  blame  those  physiologists  and  agri- 
culturists who  had  objected  that  chemistry  could 
and  did  give  them  no  answer  to  their  questions,  when 
they  had  not  learned  the  language  of  the  instrument, 
and  hence  were  unable  to  put  the  questions  to  which 
they  desired  to  have  answers. 

Has  not  Liebig,  by  his  teachings  on  this  point, 
answered  beforehand  very  plainly  a  question  which  we 
often  hear  nowadays — What  is  technical  education  ? 


188  JUSTUS   VON   LIEBIG: 

Does  it  mean  the  teaching  of  the  arts,  or  does  it 
mean  teaching  the  sciences  on  which  those  arts  are 
based  ?  And  again,  as  regards  these  sciences,  may  a 
technical  student  learn  only  just  so  much  of  them  as 
directly  applies  to  his  art;  or  must  he,  like  other 
students,  aim  at  the  best  all-round  knowledge  of  them 
that  he  can  attain  ? 

Of  course  it  is  obvious  that  if  a  youth  is  to 
become  a  baker  he  must  learn  baking  in  the  bake- 
house ;  that  if  he  would  be  an  industrial  chemist  he 
must  sooner  or  later  enter  a  chemical  works  ;  that  he 
who  would  be  a  farmer  must  spend  years  upon  a 
farm. 

For  the  rest,  what  Liebig  wrote  in  1851  still 
conveys  the  whole  truth  in  1894 — 

"  Hitherto,"  said  Liebig,  "  scarcely  any  demand 
has  been  made  upon  the  science  of  chemistry*  by 
arts,  manufactures,  or  physiology,  which  has  not  been 
responded  to.  Every  question  clearly  and  definitely 
put  has  been  satisfactorily  answered.  Only  when  the 
inquirer  had  no  precise  idea  of  the  problem  to  be 
solved  has  he  remained  unsatisfied." 

Clear  and  precise  problems  can  only  be  put  in 
chemistry  and  the  other  experimental  sciences,  as  in 
mathematics,  by  those  who  are  well  acquainted  with 
their  method  and  language,  and  who  have  learned 
how  to  set  such  problems. 

It  follows  that  he  who,  "in  these  cruel  times," 
would  take  advantage  of  the  resources  of  science  in 
his  art,  must  study  the  sciences  on  which  it  depends, 
so  far  as  he  can,  in  the  same  way  as  other  students. 
That  is  to  say,  he  must  learn  the  "  go  "  of  each  instru- 

*  He  was  then  speaking  for  chemistry  only,  but  his  words  are  not 
less  true  of  other  sciences. 


HIS    LIFE   AND   WORK.  189 

ment  as  a  whole  ;  he  must  not  be  satisfied  with  a  peep 
at  this  part  and  a  peep  at  that  part.  Above  all,  his 
scientific  training  must  cultivate  his  powers  of  obser- 
vation and  his  powers  of  putting  questions  to  nature 
to  the  utmost  possible  extent.  The  needs  of  the 
technical  student,  in  short,  do  not  differ  essentially 
at  the  early  stages  from  the  needs  of  those  who  will 
afterwards  devote  themselves  to  pure  science. 

Liebig  on  several  occasions  did  good  service  by 
helping  to  dispel  popular  errors.  This  was  notably 
the  case  in  regard  to  the  "  spontaneous  combustion  " 
question. 

In  one  of  those  delightful  discourses,  the  "  Familiar 
Letters,"  Liebig  treated  of  the  at  one  time  much  dis- 
cussed question,  Is  it  possible  for  a  human  body 
to  ignite  spontaneously  ?  The  notion  that  a  living 
human  body  is  capable  of  spontaneously  catching 
lire  appears  to  be  comparatively  modern.  The 
earliest  recorded  example  which  Liebig  could  dis- 
cover was  said  to  have  occurred  in  1725.  A 
woman  of  Rheims  was  found  half  a  yard  from  a  fire- 
place burnt  to  death  ;  very  little  was  left  of  her.  Her 
husband  had  an  attractive  servant  girl,  and  murder 
was  suspected.  But  at  the  trial  learned  experts  de- 
clared spontaneous  combustion  to  be  possible,  and  the 
husband  was  pronounced  innocent. 

This  idea,  therefore,  arose  before  Lavoisier  had 
explained  the  nature  of  combustion,  and  when  men 
were  not  in  a  position  to  understand  such  pheno- 
mena. It  persisted,  however,  long  after  Lavoisier  had 
explained  the  chemistry  of  fire.  And  Liebig  himself 
on  one  occasion  was  called  as  a  witness,  when  this  delu- 
sion had  been  set  up  in  defence  of  a  man-servant  who 
was  accused  of  the  murder  of  his  mistress,  the  Countess 


190  JUSTUS  VON  LIEBIG: 

of  Gorlitz,  in  Darmstadt,  From  1725  till  Liebig  in- 
vestigated the  subject — that  is,  during  rather  more 
than  a  century — some  forty-eight  cases  of  supposed 
spontaneous  combustion  had  been  recorded  ;  and  so 
firmly  fixed  was  the  belief  in  the  possibility  of  the 
phenomenon,  that  even  after  Liebig  had  demonstrated 
the  complete  absence  of  any  real  evidence  in  sup- 
port of  its  truth,  and  after  it  had  been  finally  aban- 
doned by  men  of  science,  and  had  ceased  to  be  ad- 
mitted in  the  law  courts,  it  retained  a  sufficient  hold 
to  be  still  made  use  of  in  fiction ;  and  Charles  Dickens, 
indeed,  published  a  defence  of  one  form  of  the  doctrine 
in  the  preface  to  an  edition  of  "  Bleak  House." 

It  need  scarcely  be  said  that  Liebig  was  not  the 
first  to  feel  doubtful  as  to  the  possibility  of  this  extra- 
ordinary phenomenon.  Others  before  him  had  rejected 
the  popular  idea  as  improbable  and  incredible ;  but 
till  Liebig's  arguments  at  length  exploded  the  belief 
it  remained  floating  in  the  heads  of  some  doctors  and 
lawyers,  and  it  was  accepted  by  them  as  at  least  an 
open  question. 

Liebig  found,  on  investigating  the  history  of  the 
recorded  cases,  that  on  most  occasions  the  victims 
were  intoxicated ;  that  the  supposed  spontaneous 
combustion  occurred  usually  where  the  rooms  are 
heated  by  open  fires  or  pans  of  glowing  charcoal, 
and  were  rare  in  countries  like  Germany,  where 
closed  stoves  are  employed ;  that  they  occurred  in 
winter ;  that  no  trustworthy  witness  had  ever  yet 
seen  the  phenomenon  occur  ;  that  the  physicians  who 
collected  the  data  had  never  really  known  the  history 
of  the  cases  they  attempted  to  explain ;  and  that 
the  amount  of  combustible  matter  on  the  spot  was 
never  ascertained.  When  he  came  to  look  into  one  of 


HlS    LIFE    AND    WORK.  191 

certain  cases  which  were  specially  reserved,  as  seeming 
to  be  established  by  Dr.  Franck,  he  found,  omitting 
many  corroborative  circumstances,  that,  in  this  case, 
before  the  combustion  took  place,  there  was  a  lamp  full 
of  oil  in  the  room,  and  afterwards  the  lamp  was  empty 
and  the  wick  burnt  up ;  that  the  body  was  only  burnt 
where  the  clothes  were  also  burnt ;  finally,  that  while 
the  clothes  were  in  many  parts  burnt  to  ashes,  the 
skin  Avas  only  detached,  hanging  in  shreds ;  from 
which  it  would  seem  to  follow,  if  spontaneous  com- 
bustion had  occurred,  that  the  kindling  of  the  clothes 
was  caused  by  the  skin,  which  yet  itself  did  not  burn. 
A  great  many  writers  in  Liebig's  time,  perhaps 
the  majority,  did  not,  however,  suppose  that  in 
these  forty-five  or  forty-eight  cases  the  victims  had 
really  ignited  spontaneously — had  caught  fire,  that 
is  to  say — without  the  aid  of  an  external  flame. 
The  most  commonly-accepted  view  was  rather  that, 
though  the  healthy  human  body  is  very  difficult  to 
burn,  the  flesh  and  skin  may  become  much  more 
combustible  through  diseased  conditions  produced, 
for  example,  by  the  excessive  use  of  strong  spirits ; 
that  they  may  become  not  merely  like  a  block  of 
wood,  which  easily  goes  out  when  kindled,  but  more 
like,  let  us  say,  tinder,  which,  when  once  ignited, 
continues  to  burn.  The  supporters  of  the  theory 
said  that  the  fact  of  spontaneous  combustion  in  this 
sense  was  not  refuted  by  all  that  science  then  knew ; 
that  circumstances  and  facts  were  quite  concordant 
with  this  view ;  and  they  asked  whether,  considering 
how  many  phenomena  there  are  which  science  has 
not  yet  explained,  it  was  fair  or  decent  to  reject  the 
testimony  of  so  many  upright  men  who  have  avowed 
their  belief  ia  spontaneous  combustion,  and  to  class 


192  JUSTUS   VON  LIEBIG  f 

them  with  liars  or  blockheads   because   we   do   not 
agree  with  them. 

Liebig  pointed  out,  in  reply  to  this,  that  nobody 
denied  the  facts  stated — viz.  that  a  number  of 
people  had  been  burnt ;  what  was  denied  was  the 
hypothesis  by  which  the  facts  were  accounted  for. 
It  was  plain  that  every  kind  of  assertion  could  be 
supported  on  such  grounds  as  these.  And,  moreover, 
that  the  opinion  that  a  man  can  burn  of  himself  was 
obviously  not  founded  on  a  knowledge  of  the  exact 
circumstances  of  death,  but,  on  the  contrary,  was 
based  upon  ignorance  of  these  circumstances. 

A  man  or  woman  is  found  in  a  room  burned 
to  death.  The  experts,  after  an  inquiry,  cannot  dis- 
cover how  the  fire  originated,  or  how  it  was  propagated 
in  the  body ;  therefore,  because  at  intervals  during 
a  century  or  more  in  the  past  similar  unaccount- 
able deaths  from  fire  have  occurred,  and  have  been 
ascribed  to  spontaneous  combustion,  we  are  asked  to 
ascribe  these  deaths  also  to  the  same  cause.  And  this 
in  spite  of  the  fact  that  our  predecessors  appear  to 
have  been  quite  as  ignorant  as  ourselves  of  the  facts 
of  the  respective  cases,  were  not  even  present  at  the 
time  of  the  occurrences,  and  that  their  explanation 
is  not  only  without  any  independent  support  of  a 
definite  kind,  but  also  contradicts  all  that  we  know 
about  the  combustibility  of  animal  matter. 

Before  it  can  be  admitted  that  a  given  death  by 
fire  was  due  to  the  body  having  acquired  a  morbid 
state,  in  which  it  becomes  as  combustible  as  straw, 
we  must,  said  Liebig,  "not  only  prove  that  it  is 
possible  for  a  piece  of  flesh  to  become  thus  com- 
bustible, but  we  must  prove  that  such  combustion, 
when  it  occurred,  has  proceeded  from  the  flesh 


HIS    LIFE    AND    WORK.  193 

outwards  ...  it  must  be  shown  that  a  morbid 
state,  such  as  is  assumed,  actually  exists  ;  and  further, 
that  the  persons  who  were  burned  were  in  that 
morbid  condition." 

"  Xow,  nothing  of  the  kind  has  ever  been  done ; 
no  doctor  has  ever  observed  a  condition  of  the 
human  body  in  which  it  was  readily  combustible; 
and  no  one  knows  any  signs  by  which  we  could 
recognise  such  a  condition." 

In  concluding  this  letter  Liebig  made  a  valuable 
contribution  to  medical  jurisprudence,  which,  though 
it  related  only  to  the  question  of  spontaneous  com- 
bustion, upheld  a  really  important  principle. 

The  physician,  he  said,  "  who  is  called  on  for 
a  judgment  in  such  cases  can  only  say,  if  he  act 
according  to  duty  and  conscience,  in  what  state  the 
body  was  found ;  whether  the  injury  from  burning 
took  place  before  or  after  death ;  whether  death  was 
caused  by  fire  alone,  or  before  the  action  of  the  fire 
by  other  causes,  such  as  wounds,  strangulation,  a  blow 
on  the  head,  etc.  In  no  case  is  it  permitted  him  to 
explain  anything  he  has  not  seen  by  cases  which  he 
has  also  not  seen,  or  by  a  theory  which  he  cannot 
understand."  Those  who  disregard  these  limitations 
protect  criminals,  and  delay  or  prevent  the  adminis- 
tering of  justice. 

The  comparative  ease  with  which  Liebig  over- 
threw this  popular  fallacy  throws  an  interesting 
sidelight  on  the  progress  of  civilisation  in  Europe. 
It  had  now  become  not  only  safe  to  attack  a  popular 
error,  but  one  might  even  hope  to  destroy  it.  This  was 
not  so  a  little  earlier.  We  are  told  that  when  Kepler 
the  astronomer  went  to  Tubingen,  in  the  sixteenth 
century,  to  save  his  mother  from  the  stake,  he 

M 


194  JUSTUS   VON   LIEBIG  : 

succeeded  not  by  proving  that  there  are  no  such  people 
as  witches,  but  only  by  showing  that  she  possessed  none 
of  the  characteristic  signs  essential  to  a  witch. 

This  was  not  the  only  occasion  on  which  Liebig 
set  himself  to  correct  popular  misconceptions.  Thus 
when,  after  the  discovery  of  electro-magnetism,  his  less 
instructed  countrymen  were  pleasing  themselves  with 
the  idea  that  electricity  would  replace  steam  for  putting 
machinery  in  motion,  and  that,  because  zinc  is  used  for 
generating  electricity,  and  is  plentiful  in  Germany, 
soon  Germany  would  become  the  chief  seat  of  the 
manufactures  in  place  of  England,  Liebig  was  quick  to 
point  out  to  them  that  such  expectations,  though 
attractive  to  the  human  mind,  are  quite  fallacious, 
unless  they  are  the  outcome  of  exact  comparisons  and 
calculations.  "  Out  of  nothing,"  said  Liebig,  "  no  kind 
of  force  can  arise."  From  a  pound  of  coal  we  get  about 
six  times  as  much  force  as  from  a  pound  of  zinc  when 
we  burn  them,  and  hence,  even  if  it  were  true  that  the 
latter  produces  four  times  as  much  force  in  a  galvanic 
pile  as  it  does  when  we  burn  it,  the  coal  would  still  be 
the  more  economical  substance  in  practice.  Besides, 
coal  is  wanted  to  reduce  zinc  from  its  ores,  and  it 
is  probable  that,  if  the  coal  required  for  smelting  the 
zinc  were  burned  under  a  stearn-engine,  we  should 
obtain  much  more  force  than  all  that  the  zinc  reduced 
by  means  of  it  could  yield  us. 

These  are  a  few  illustrations  drawn  from  this  re- 
markable book,  into  which  Liebig  put  so  much  of  his 
very  best  work  and  thought  in  a  form  in  which  they 
could  help  every  intelligent  person  who  would  read 
them.  They  are,  as  Liebig  meant  them  to  be,  a  great 
deal  more  than  mere  popular  expositions.  In  these 
letters  science  is  freed  from  technicalities,  but  Liebig 


HIS    LIFE   AND   WORK.  195 

did   not  allow   himself   to  attenuate  the  science   in 
getting  rid  of  the  technicalities. 

It  has  been  necessary  in  the  preceding  pages  to 
refer  to  several  of  Liebig's  most  important  books,  and 
it  has  been  mentioned  that  the  mere  list  of  his 
memoirs  to  scientific  journals  occupies  twenty- three 
columns  of  the  Royal  Society's  catalogue,  and  in- 
cludes 318  separate  papers;  but  this  does  not  give 
anything  like  a  sufficient  idea  of  his  immense  con- 
tributions to,  and  influence  on,  scientific  literature. 
In  1832  he  founded  one  of  the  most  celebrated  of 
scientific  periodicals,  known  generally  as  the  Annalen, 
in  the  editing  of  which  he  had  for  a  long  while  the 
assistance  of  his  friend  Friedrich  Wohler  and  of  Her- 
mann Kopp,  the  historian  of  chemistry.  It  may  be 
imagined  what  this  alone  meant  when  it  is  said  that 
no  less  than  165  volumes  of  the  book  had  appeared 
at  the  time  of  Liebig's  death  in  1873.  In  the 
Annalen  are  to  be  found  all  the  researches  carried  out 
by  Liebig  and  by  his  pupils  at  Giessen,  from  the  time 
of  their  first  publication.  Jointly  with  Wohler  again, 
and  with  the  co-operation  of  Poggendorff,  he  was 
author  of  a  dictionary  of  pure  and  applied  chemistry, 
which  was  for  long  a  most  valuable  resource,  and  on 
which  a  later  dictionary  by  Fehling  was  founded. 
Besides  this  he  gave  chemists  the  benefit  of  his 
unexampled  mastery  of  organic  chemistry  in  his 
handbook  on  that  subject,  the  origin  of  which  did  as 
much  credit  to  his  heart  as  its  execution  did  to  his 
head.  It  appears  that  shortly  after  the  death  of  an 
early  friend,  P.  L.  Geiger,  a  new  edition  of  his  once 
celebrated  book  on  pharmacy — "Geiger's  Handbook 
of  Pharmacy  " — was  called  for,  and  that  Liebig,  with 
characteristic  generosity,  undertook  to  revise  the 


196  JUSTUS  VON    LIEBiG  : 

chemical  part  of  it  in  the  interest  of  his  dead 
friend's  widow.  Soon,  however,  revision  was  found 
to  be  impossible;  so  great  were  the  strides  which 
chemistry  had  made  in  the  interval  since  Geiger 
had  published  his  last  volume,  that  Liebig  had  to 
give  up  the  idea  of  revising  the  work,  and  pro- 
ceeded to  re-write  it,  with  the  result  that  the  new 
"  Handbook  of  Organic  Chemistry "  soon  appeared. 
This  book  had  a  wonderful  success ;  what  had  previ- 
ously been  a  maze  of  incoherent  information  be- 
came in  this  volume  for  the  first  time  an  articulated 
science,  it  was  soon  translated  into  French  and 
appeared  also  in  England  as  a  part  of  Turner's 
"  Chemistry  "  in  the  later  editions  of  that  work. 

On  the  death  of  Berzelius,  he  was  called  by 
the  unanimous  voice  of  chemistry  to  continue  the 
Annual  Reports  on  the  progress  of  chemical  science 
which  Berzelius  had  for  many  years  drawn  up. 
When  it  is  mentioned  that  for  the  compiling  of 
these  reports  the  work  of  a  small  army  of  in- 
vestigators, published  in  perhaps  a  hundred  jour- 
nals, and  in  several  languages,  had  to  be  read  and 
sifted,  it  will  be  understood  what  a  labour  this  work 
must  have  involved,  and  how  great  a  service  Liebig 
did  his  fellow  chemists  by  undertaking  it.  And 
even  when  all  this  is  told,  there  remain  his  various 
discourses  on  subjects  of  popular  interest,  his  re- 
ports (1)  On  the  State  of  Chemistry  in  Austria, 
and  (2)  On  the  State  of  Chemistry  in  Prussia, 
which  exercised  a  most  marked  influence  on  the 
progress  of  scientific  education  in  Germany ;  and 
some  minor  books  and  pamphlets,  enough  by  them- 
selves to  have  made  a  great  reputation. 


HIS    LIFE    AND  WORK.  197 


CHAPTER   IX. 

CHARACTER  AND  LATER  YEARS. 

Dominant  Characteristics  of  Liebig — Address  to  Bavarian  Academy 
after  Franco- Prussian  War — Relations  with  English  Men  of 
Science— Letter  to  Faraday — A  Testimonial  from  England — 
Liebig  and  his  pupils — Munich  and  his  later  years. 

THE  dominant  characteristics  of  Liebig  were  his 
intense  desire  for  truth,  his  unselfishness,  the  com- 
plete absence  from  his  mind  of  any  tincture  of  the 
partisan,  and  his  unfailing  vivacity. 

His  scientific  disputes  were,  from  the  novelty  of 
many  of  his  ideas,  not,  unnaturally,  rather  numerous. 
In  scientific  discussions  he  too  often  forgot  the  man 
in  his  desire  to  rend  and  destroy  the  error.  In  his 
ardour  he  doubtless  sometimes  forgot  that  his  oppo- 
nents, like  himself,  were  animated,  in  most  cases  at 
least,  by  a  desire  to  promote  the  discovery  of  truth 
and  the  overthrow  of  error.  But  there  was  so  much 
to  admire  in  Liebig,  so  much  to  love  when  you 
knew  him — and  he  was  so  ready  to  admire  what  he 
saw  to  be  true  even  in  the  work  of  an  opponent — that 
when  the  battle  was  once  fought  out  reconciliation 
was  in  most  cases  easy;  and  we  find,  for  example, 
that,  in  spite  of  the  vivacity  of  his  encounters  with 
Dumas,  these  two  great  men  were  more  than  once 
to  be  found  working  together.  And  again,  that  hi 
spite  of  the  discussions  with  Laurent  and  Gerhardt,^in 
which  Liebig  took  an  active  part,  and  in  which  the 
two  former  chemists  had  to  suffer  treatment  which 


198  JUSTUS   VON   LIEBIG: 

has  since  been  described  as  "  quite  painful  to  think 
of,"  Gerhardt  described  his  meeting  with  Liebig  at 
Munich  some  time  afterwards  to  Hofmann  with 
"  glowing  delight." 

Nor  must  we  forget,  when  reading  Liebig's  most 
lively  passages,  that  they  were  not  written  yesterday. 
Neither  in  pugilistic  encounters,  nor  in  scientific 
disputes,  had  it  then  become  the  custom  to  fight  with 
the  gloves  on ;  and,  besides,  his  antagonists  were  by 
no  means  unable  or  unwilling  to  give  very  hard 
knocks  themselves  when  an  opportunity  arose. 

Liebig  was  one  of  the  first  eminent  Germans  after 
the  Franco-Prussian  War  to  hold  out  the  olive  branch. 
At  a  moment  when  the  irritation  on  both  sides  was 
still  keen,  he  attempted,  in  an  address  to  the  Bavarian 
Academy,  to  soothe  the  feelings  of  the  moment  by  an 
eloquent  appeal  to  the  traditions  of  the  glorious  past. 

"  This,"  said  Liebig,  "  is,  perhaps,  a  fit  opportunity 
for  declaring,  on  the  part  of  our  Academy,  that  a 
hatred  of  race  between  the  German  and  Latin  nations 
does  not  exist. 

"  We  look  on  the  heavy  affliction  which  in  former 
times  the  French  nation  has  caused  to  Germany  as 
on  an  illness,  the  pains  of  which  are  utterly  forgotten 
with  the  return  of  health. 

"  The  peculiar  nature  of  the  German,  his  know- 
ledge of  languages,  his  appreciation  of  other  nationali- 
ties, compel  him  to  do  justice  to  foreigners,  so  much 
so  as  occasionally  to  become  unjust  to  himself;  and 
thus  we  cannot  possibly  underrate  the  debt  of 
gratitude  we  owe  to  the  great  philosophers,  mathe- 
maticians, and  natural  inquirers  of  France,  who,  in 
so  many  departments,  have  been  our  masters  and 
exemplars 


HIS   LIFE    AND    WORK.  199 

"  Warm  sympathy  for  all  that  is  noble  and  great, 
and  disinterested  hospitality,  are  among  the  finest 
features  of  the  French  character.  It  will  be  on 
the  neutral  ground  of  science  that  the  best  minds 
of  the  two  nations  must  meet  in  endeavouring 
to  reach  the  high  goal  common  to  both,  that 
these  sentiments  will  be  again  kindled  into  life 
and  activity;  and  thus  the  feeling  of  fraternity  in 
science,  which  can  never  be  entirely  extinguished,  will 
gradually  contribute  to  mitigate  the  bitterness  with 
which  the  deeply  wounded  national  pride  of  the 
French  is  filled  by  the  consequences  of  the  war  they 
have  forced  upon  us." 

The  last  few  words  might  have  been  different, 
but  they  were  said  in  1871.  The  rest  formed  a 
characteristic  tribute  to  the  nation  who  had  fostered 
and  helped  to  inspire  Liebig  himself  half  a  century 
before. 

Liebig's  relations  with  the  English  men  of  science 
were  of  the  most  cordial  character.  After  his  first 
visit  to  England,  in  1837,  he  wrote  on  his  return 
that  he  had  seen  astonishing  things.  At  that  tune 
Thomas  Graham  alone,  among  the  chemists,  made  a 
very  strong  impression  on  him,  and  he  noted  with 
regret  that  the  opportunities  for  learning  chemistry 
were  then  bad.  English  students  went  to  Germany 
in  large  numbers  to  become  his  pupils.  Two  of  the 
most  important  of  his  works  were  presented  to  the 
British  Association,  as  we  have  seen,  and  most  of  his 
other  books  were  translated  into  our  language;  con- 
sequently his  influence  on  the  progress  of  chemistry 
in  this  country  has  been  very  great.  In  the  course 
of  his  repeated  visits  he  became  acquainted  with 
Faraday,  for  whom  he  conceived  feelings  of  the  most 


200  JUSTUS   VON  L1EBIG: 

profound  admiration,  respect,  and  friendship.  The 
following  letter  from  Liebig  to  Faraday  is  interesting 
alike  for  the  light  it  throws  on  the  relations  between 
these  two  great  men,  and  for  the  delightful  picture, 
mere  sketch  though  it  be,  which  it  contains  of 
Liebig's  home  life  in  Giessen : — 

"  GIESSEN,  December  19th,  1844. 

"DEAR  FARADAY, — I  intended  to  have  written  you  long 
ago  of  my  safe  arrival,  and  that  I  had  found  my  wife  and 
children  well.  The  opening  of  my  winter  course,  and  a  mass  of 
work  which  had  accumulated  during  my  absence,  have  hitherto 
prevented  my  fulfilling  my  intentions.  Now,  however,  that  I 
have  a  few  days  of  rest  during  the  Christmas  holidays,  I  will 
not  let  the  opportunity  slip  of  wishing  you,  with  my  whole  heart, 
a  merry  Christmas  aud  a  happy  new  year.  Often  do  my  thoughts 
wander  back  to  the  period  which  I  spent  in  England ;  among  the 
many  pleasant  hours  of  which  the  remembrance  of  those  passed 
with  you  and  your  amiable  wife  is  to  me  always  the  dearest  and 
most  agreeable.  With  the  purest  pleasure  I  bring  to  mind  my  walk 
with  her  in  the  Botanical  Garden,  at  York,  when  I  was  afforded 
a  glance  of  the  richness  of  her  mind :  what  a  rare  treasure  you 
possess  in  her  !  The  breakfast  in  the  little  house  with  Snow- 
Harris  and  Graham,  and  our  being  together  at  Bishopthorpe, 
are  still  fresh  in  my  memory.  I  wish  it  were  only  my  good 
fortune  to  see  and  talk  with  you  ofteuer,  and  to  exchange  ideas 
with  you. 

"Nature  has  bestowed  on  you  a  wonderfully  active  mind, 
which  takes  a  lively  share  in  everything  that  relates  to  science. 
Many  years  ago  your  works  imparted  to  me  the  highest  regard 
for  you,  which  has  continually  increased  as  I  grew  up  in  years 
and  ripened  in  judgment ;  and  now  that  I  have  had  the  pleasure 
of  making  your  personal  acquaintance,  and  seeing  that  in  your 
character  as  a  man  you  stand  as  high  as  you  do  in  science,  a 
feeling  of  the  greatest  affection  and  esteem  has  been  added 
to  my  admiration.  You  may  hence  conceive  how  grateful  I 
am  for  the  proof  of  friendship  which  you  have  given  me. 

"  I  have  every  reason  to  be  satisfied  with  my  journey  in 
Great  Britain  :  rare  proofs  of  recognition  have  indeed  been  given 


HIS    LIFE    AND   WORK.  201 

me.  What  struck  me  most  in  England  was  the  perception  that 
only  those  works  which  have  a  practical  tendency  awake  atten- 
tion and  command  respect,  while  the  purely  scientific  works, 
which  possess  far  greater  merit,  are  almost  unknown.  And  yet 
the  latter  are  the  proper  aud  true  source  from  which  the  others 
flow.  Practice  alone  can  never  lead  to  the  discovery  of  a  truth 
or  a  principle.  In  Germany  it  is  quite  the  contrary.  Here,  in 
the  eyes  of  scientific  men,  no  value,  or,  at  least,  but  a  trifling  one, 
is  placed  on  the  practical  results.  The  enrichment  of  science 
is  alone  considered  worthy  of  attention.  I  do  not  mean  to  say 
that  this  is  better ;  for  both  nations  the  golden  medium  would 
certainly  be  a  real  good  fortune. 

"  The  meeting  at  York,  which  was  very  interesting  to  me  from 
the  acquaintance  of  so  many  celebrated  men,  did  not  satisfy  me 
in  a  scientific  point  of  view.  It  was  properly  a  feast  given  to 
the  geologists,  the  other  sciences  serving  only  to  decorate  the 
table.  The  direction,  too,  taken  by  the  geologists  appeared  to 
me  singular,  for  in  most  of  them,  even  the  greatest,  I  found  only 
an  empirical  knowledge  of  stones  and  rocks,  of  some  petrifacts 
and  a  few  plants,  but  no  science.  Without  a  thorough  knowledge 
of  physics  and  chemistry,  even  without  mineralogy,  a  man  can 
be  a  great  geologist  in  England. 

"I  saw  a  great  value  laid  on  the  presence  of  petrefactions 
and  plants  in  fossils,  whilst  they  either  do  not  know  or  con- 
sider at  all  the  chemical  elements  of  the  fossils — those  very 
elements  which  made  them  what  they  are. 

"  This  letter  has  already  grown  too  long,  and  truly  I  fear  to 
weary  your  patience.  I  cannot,  however,  deny  myself  the  pleasure 
of  expressing  a  sincere  wish  to  see  you  and  your  wife  here  in 
Giessen  next  summer.  Did  you  know  how  quietly  we  live  at 
our  German  universities  you  would  certainly  expect  from  your 
visit  only  benefit  to  your  health.  Except  scientific  pursuits  we 
have  no  other  excitements  of  the  mind.  We  take  walks  in  our 
beautiful  green  woods,  and  in  the  evening  drink  tea  at  the  neigh- 
bouring old  castles.  This  is  our  recreation.  I  beg  of  you,  dear 
Faraday,  to  listen  to  niy  request.  I  pray  your  dear  wife  to 
assist  me  in  trying  to  make  you  decide  on  this  journey.  My 
wife  unites  with  me  in  begging  this,  it  would  give  her  the 
greatest  pleasure  to  make  the  personal  acquaintance  of  you  and 
your  lady. 


202  JUSTUS   VON   LIEBIG: 

"  Farewell,  dear  Faraday,  preserve  to  ine  your  friendly 
favour,  and  believe  me,  with  all  sincerity,  to  be 

"  Tours  very  truly, 

"DR.  JTJST.  LIEBIG." 

One  cannot  help  seeing  in  this  letter  a  charming 
simplicity  of  mind  which  reminds  one  of  Faraday 
himself.  Different  as  these  two  men  were,  in  many 
respects,  they  resembled  one  another  in  this,  and 
in  a  certain  modesty,  which  was  never  out  of  sight 
in  the  case  of  Faraday,  and  showed  itself  in  Liebig, 
too,  upon  occasion — as,  for  example,  when,  as  a  young 
man,  he  wrote  to  Wohler,  in  1830,  regretting  that  they 
had  never  yet  met,  and  expressed  a  fear  that  Wohler 
would  find  out  later  his  (Liebig's)  real  poverty  of 
acquired  knowledge — and  which  led  him  to  say  so 
little  about  the  various  scientific  distinctions  which 
were  liberally  showered  upon  him,  even  before  he 
reached  middle  life,  that  frequently  many  of  his  in- 
timate friends  were  unaware  that  he  had  received 
them.  Nor  was  this  silence  due  to  want  of  appre- 
ciation. This  is  shown  by  the  correspondence  given 
below,  which  took  place  on  the  occasion  of  his  accept- 
ing the  call  to  Munich,  when  Liebig's  English  friends 
united,  under  the  presidency  of  Graham,  to  recognise 
the  occasion  by  presenting  a  testimonial  to  him : — 

"  LONDON,  July,  1854. 

"  SIR,  —Your  retirement  from  the  Chair  of  Chemistry  in  the 
University  of  Giessen  has  appeared  to  many  in  this  country 
a  fitting  occasion  for  the  public  acknowledgment  of  your 
eminent  scientific  services.  Accordingly  a  numerous  body  of 
your  friends  aud  admirers  have  united  to  present  to  you  a 
Testimonial,  commemorative  of  their  profound  and  unalterable 
regard.  In  the  list  of  subscribers  hereto  annexed,  you  will 
recognise,  with  those  of  your  pupils  and  personal  friendSj 
the  names  of  many  other  gentlemen  eminent  in  science,  in 


HIS    LIFE    AND   WORK.  203 

social    position,   and   in  the  practical   arts   of  life,  who  were 
anxious  to  join  in  this  jnst  tribute  to  your  merit. 

"In  presenting  to  you  this  Testimonial,  the  subscribers 
desire  to  express  their  sense  of  the  benefits  which  your  genius 
and  labours  have  conferred  upon  mankind  in  adding  to  the 
world's  stock  of  positive  knowledge.  These  benefits  are  limited 
to  no  one  people  or  time ;  but  it  is  felt  that  Englishmen  may,  with 
propriety,  take  the  lead  upon  this  occasion,  as  the  impulse  which 
you  have  given  to  chemical  science  has  been  experienced 
especially  in  England.  More  students  from  this  country  than 
from  any  other  laud  beyond  the  bounds  of  Germany,  have 
worked  in  the  laboratory  of  Giessen,  and  have  derived  incal- 
culable benefit  from  the  instruction  there  imparted,  and  from 
the  noble  example  there  presented  to  them  of  an  elevated  philo- 
sophical and  scientific  life.  In  England,  also,  have  the  applica- 
tions which  you  have  made  of  chemical  science  to  the  cultivation 
of  the  soil  been  peculiarly  appreciated  and  adopted. 

"  Your  discoveries  in  practical  agriculture  have  enriched  the 
laud,  aiid  with  you  originated  the  method  of  scientific  inquiry 
which  is  here  pursued  on  an  extended  scale  by  numerous  investi- 
gators, and  which  is  rapidly  changing  the  features  of  the  most 
ancient  and  important  of  human  arts. 

"  We  earnestly  hope  that  your  life,  which  has  been  devoted  to 
the  highest  aims  to  which  man  can  aspire,  may  be  prolonged  to 
many  years  of  happiness  and  honour. 

"  Signed  on  behalf  of  the  subscribers, 

"THOMAS  GRAHAM. 

"  To  Baron  Liebig." 

Liebig's  reply : — 

"MUNICH,  July  20th,  1854. 

'•  SIR, — The  man  of  science  generally  knows  of  no  other 
reward  for  the  time  he  has  devoted  to  the  discovery  of  trnth 
and  to  the  investigation  of  the  laws  of  Nature's  powers,  than 
the  mental  satisfaction  which  springs  from  the  consciousness  of 
having,  to  the  best  of  his  ability,  contributed  his  part  towards 
the  advancement  of  human  happiness  and  human  welfare ;  for 
toils  like  his,  attended  as  they  are  with  so  many  difficulties  and 
sacrifices,  and  with  such  mental  effort,  and  fatigue,  cannot  be 
priced  in  the  market  or  sold — cannot  be  performed  to  order, 


204  JUSTUS   VON    LIEBIG: 

or  turned  into  money.  If  he  has  been  fortunate  enough  to  have 
gained  by  his  successes  the  acknowledgment  and  esteem  of  his 
contemporaries,  he  has  obtained  the  highest  object  of  his  ambition. 

"  If  I  have  laboured  for  the  period  of  almost  a  human  life  in 
promoting  the  progress  of  chemistry,  and  in  making  its  principles 
subservient  and  useful  to  other  branches  of  knowledge,  more 
especially  to  the  industrial  arts  and  to  agriculture.  I  gratefully 
acknowledge  that  I  have  received  in  return  all  that  a  man  could 
justly  aim  at.  My  satisfaction  in  this  respect  is  not  a  little 
enhanced  when  I  look  back  to  the  number  of  zealous  and  able 
men  in  whose  education  I  have  been  enabled  to  assist,  and  who  are 
now  occupying,  in  various  countries,  a  distinguished  position  in 
the  front  rank  of  Science,  and  are,  with  splendid  success,  culti- 
vating and  extending  her  domains — teaching,  diffusing,  and 
successfully  applying  those  principles  of  investigation  which  con- 
stitute the  true  foundations  of  scientific  progress.  It  is  with 
pride  that  I  am  able  to  add  that  in  these  my  former  pupils 
I  have  gained  an  equal  number  of  warm  friends,  who,  I  am 
sure,  look  back  with  pleasure  to  the  time  when  we  combined 
our  powers  in  one  common  aim  and  effort. 

"  And  now,  in  addition  to  all  that  a  benevolent  destiny  had 
already  granted  me  in  measure  above  many,  I  receive  from  my 
friends  in  England,  in  this  gift  of  friendship,  in  this  testimonial 
of  honour,  a  token  and  a  proof  of  their  recognition  and  approbation 
of  my  labours. 

"  When  I  reflect  that  whatever  of  good  a  man  accomplishes 
flows  from  an  inner  impulse  of  which  he  is  often  but  imperfectly 
conscious,  and  that  a  higher  power  has  a  part  in  all  his  labours 
and  usefulness— giving  to  them  their  life-germ  and  their  capacity 
of  growth,  I  must  own  that  in  receiving  this  noble  Present  I  am 
blessed  far  beyond  my  deserts. 

"I  feel  myself  in  the  highest  degree  honoured  and  most 
deeply  touched  by  this  substantial  and  permanent  expression  of 
the  kind  feelings  of  my  friends  in  England.  Convey  to  them 
all  my  best  and  warmest  thanks.  This  Gift  of  Honour  possesses 
for  me  inestimable  value,  and  will  remain  a  lasting  memorial  in 
my  family.  "  DR.  JUSTUS  VON  LIEBIG. 

"To  Thomas  Graham,  Esq." 

In  his  private  life  Liebig's  character  showed  the 


HIS   LIFE    AND    WORK.  205 

same  simplicity  and  nobility  that  distinguished  him 
in  his  relations  with  Faraday,  Wohler,  and  Dumas. 
His  intercourse  with  his  pupils  was  marked,  they  tell 
us,  by  a  dignified  composure  combined  with  a  marked 
simplicity  and  kindness  which  could  not  fail  to  en- 
courage the  most  timid  beginner ;  whilst  he  gave  to 
the  assiduous  worker  a  degree  of  helpful  sympathy 
which  led  him  to  make  any  sacrifice,  and  lasted  long 
after  the  period  of  personal  intercourse.  Nor  did  he 
reserve  his  interest  and  support  for  his  own  pupils 
alone.  His  generous  instincts,  which  led  him  to  help 
these  so  unstintedly,  impelled  him  also  to  give  counsel 
or  assistance  Avherever  he  recognised  that  it  was 
deserved.  Thus,  when  Sir  Henry  Roscoe  was  a 
candidate  for  the  professorship  of  chemistry  at 
Owens  College  Liebig — who  had  become  acquainted 
with  Mr.  Roscoe  on  the  occasion  of  one  of  his  visits 
to  England — hearing  of  his  candidature  at  a  moment 
when  he  was  about  to  depart  on  a  journey,  when  the 
carriage  was,  indeed,  standing  at  his  door,  at  once 
delayed  his  departure  hi  order  to  write  a  few 
words  in  support  of  the  young  Englishman,  of  whom 
he  had  formed  a  high  opinion. 

One  more  illustration  of  the  generous  disposition 
which  prompted  Liebig  to  help,  whenever  he  saw  that 
help  was  needed,  whether  by  a  friend  or  by  a  stranger, 
will  be  welcomed,  as  it  shows  so  well  his  genuine 
goodness  of  heart. — Shortly  after  his  call  to  Munich 
(1853),  Liebig,  in  company  with  Hofmann  and  two 
other  friends,  was  making,  as  Hofmann  has  told  us, 
an  excursion  among  the  mountains  of  the  Tyrol. 

One  morning,  in  the  course  of  their  walk  they 
came  upon  an  old  soldier,  wasted  by  fatigue  and  en- 
feebled by  disease,  a  pitiable  object,  travelling  slowly 


206  JUSTUS   VON   LIEBIG  : 

along.  As  they  came  up  to  him  he  accosted  them 
with  a  piteous  tale,  asking  their  aid.  Liebig,  whose 
purse  was  always  as  readily  opened  as  his  heart,  and 
his  friends  soon  made  up  a  little  stock  of  money  for 
this  poor  wayfarer,  which  doubtless  seemed  to  him 
a  small  fortune.  They,  passing  on,  soon  reached  the 
next  village  where  they  were  to  rest  and  dine,  leaving 
the  traveller  to  follow  at  his  slower  pace,  and  presently 
he,  too,  was  observed  to  enter  the  inn.  Their  own 
meal  finished,  his  benefactors  settled  down  to  a  siesta 
before  continuing  their  journey,  soothed  by  the  re- 
flection that  for  once  the  poor  soldier  also  had  the 
means  to  procure  himself  a  substantial  meal. 

Half  an  hour  later  Hofmann  awoke.  But  where 
was  Liebig  ?  There  were  his  two  fellows  fast  asleep. 
But  where  was  their  leader  ?  Surprised  by  his  dis- 
appearance, Hofmann  at  once  got  up  and  inquired 
of  the  landlord  what  had  become  of  his  friend,  "  the 
elderly,  spare  man  of  the  party."  The  landlord  told  him 
that  a  little  while  before  the  gentleman  had  inquired 
for  a  pharmacy ;  and  on  being  told  that  there  was 
none  nearer  than  that  in  the  next  village  over  the 
hill,  he  had  set  out  in  that  direction.  By  no  means 
without  anxiety  Hofmann  forthwith  set  out  along 
the  road  Liebig  had  taken,  and  presently  saw  his 
figure  on  the  brow  of  the  hill.  Hurrying  forward, 
he  soon  met  him,  and  then  learned  that  he  had 
noticed  in  the  soldier  symptoms  of  low  fever,  such 
as  quinine  was  certain  to  cure,  and  had  been  to  the 
nearest  pharmacy  to  get  some. 

On  his  arrival  he  had  found  the  pharmacy  closed, 
and  the  apothecary  away,  but  his  wife  had  given 
Liebig  the  run  of  the  place  and  allowed  him  to  take 
what  he  liked  and  fix  his  own  price.  Fortunately 


HIS   LIFE    AND   WORK.  207 

quinine  was  in  the  stock,  and  so  his  object  was  secured, 
and  soon  the  wayfarer  was  provided  with  a  box  of 
powders  which  were  probably  sufficient  for  his  cure. 

The  incident  was  simple  enough.  But  how  many 
of  us  at  fifty  would  have  undertaken  this  extra  tramp, 
after  a  midday  dinner  and  a  long  walk,  with  another 
walk  before  us,  in  order  to  afford  succour  to  a  wayside 
beggar  ?  Could  even  those  whom  Liebig  belaboured  in 
the  arena  of  scientific  controversy  help  loving  such  a 
man  when  they  came  to  know  him,  or  fail  to  forgive 
him  if  in  his  ardour  in  the  support  of  what  he  con- 
sidered to  be  true,  he  sometimes  exceeded  the  bounds 
of  courtesy  in  scientific  warfare  ? 

Liebig  was  probably  never  what  we  should  call  a 
robust  man,  though  he  possessed  undoubtedly  very 
remarkable  powers  of  sustained  work  of  the  most 
exhausting  kind.  In  his  letters  to  Wohler  complaints 
of  ill-health  were  certainly  frequent ;  but  from  the 
amount  of  work  he  got  through,  it  seems  likely  that 
he  suffered  rather  from  occasional  malaise  than  from 
actual  illness.  For  many  years  it  seems  pretty  certain 
that  he  was  always  somewhat  overworked,  for  though 
he  was  frequent  in  his  injunctions  to  his  friend 
Wohler  to  "  throw  writing  to  the  devil,"  he  himself 
never  failed  to  respond  to  any  call  that  was  made 
upon  him  to  do  work  of  the  literary  kind.  And  we 
know,  too,  from  Wohler's  letters  that  the  discussions 
in  which  he  shared  were  no  play  to  him,  but,  while 
they  lasted,  grim  reality,  and  a  source  of  considerable 
strain,  which  told  upon  his  physical  health.  We  must 
not  regret  this,  however.  Our  science  would  have 
been  less  forward  to-day  if  Liebig  had  not  thrown 
his  whole  soul  into  those  battles  of  the  giants  which 
distinguished  the  middle  of  the  present  century. 


208  JUSTUS   VON   LIEBIG: 

After  twenty-eight  years  at  Giessen,  Liebig  was 
called  to  Munich  in  1852.  And  there,  in  spite  of  an 
invitation  to  Berlin  in  1865,  he  worked  till  the  end. 
At  Munich  Liebig  made  no  fresh  great  departures,  but 
he  continued  to  work,  following  the  lines  he  had 
already  laid  down.  The  change  from  quiet  Giessen  to 
Munich  seems  to  have  been  in  every  way  grateful  to 
him.  When  he  arrived  there,  he  found  the  new 
laboratory  was  barely  roofed  in,  he  was  without 
materials  and  apparatus,  and  there  were  new  assistants 
who  had  to  be  trained  to  his  ways ;  but,  in  spite  of  all 
difficulties,  he  was  soon  able  to  start  his  first  course  of 
lectures,  which  was  attended  by  two  hundred  and 
fifty  students,  and  at  Christmas  he  declared,  in  a 
letter  to  Wohler,  that  "  he  had  made  a  good  exchange." 

Liebig  was  persona  grata  at  the  Court  of  King 
Ludwig,  and  at  an  early  day  was  called  upon  to 
lecture  before  his  Majesty  and  some  members  of  the 
Royal  Family.  There  was  an  explosion ;  it  looked  like 
a  bad  one.  and  Liebig,  as  he  recovered  from  the  effects, 
was  horrified  to  see  blood  streaming  from  the  faces  of 
Queen  Theresa  and  Prince  Leopold.  Fortunately  their 
injuries  were  trivial ;  and  their  agitation  soon  subsided 
when  they  found  that  Liebig,  who,  of  course,  had  been 
in  the  thick  of  it,  was  also  not  seriously  damaged. 

The  advantages  gained  by  the  change  to  Munich 
were  twofold.  First,  there  was  the  wider  social  life,  in 
which  Liebig  found  much  pleasure.  Secondly,  he  was 
no  longer  called  upon  to  personally  superintend  the 
work  of  large  classes  of  students  in  practical  chemistry. 
And,  besides,  the  greater  leisure  which  he  found  in 
his  new  post  made  it  possible  for  him  to  enjoy,  more 
freely  than  before,  the  pleasures  to  be  found  in  a 
cultivated  society,  and  to  indulge  a  marked  taste  for 


HIS    LIFE    AND    WORK.  209 

general  literature,  which  we  first  hear  of  in  connec- 
tion with  the  correspondence  between  Liebig  and  his 
friend  Platen. 

As  the  years  rolled  by,  Liebig,  in  spite  of  his  pro- 
found interest  in  his  work  in  applied  science,  now  and 
then  looked  back  with  regret  on  the  early  days  at 
Giessen,  when  he  laboured  chiefly  in  pure  science. 
When  discouraged,  as  he  sometimes  was,  by  the  mis- 
conceptions of  his  opponents,  or  by  the  slowness  with 
which  many  physiologists  and  agriculturists  learned 
what  he  had  to  teach  them,  he  was  now  and  then 
tempted  to  envy  Wohler,  who  had  not  plunged  with 
him  into  these  troubled  waters,  but  remained  to 
the  end  constant  in  his  devotion  to  the  study  of 
chemistry.  It  was  in  such  a  mood  that  in  1857  he 
wrote  to  Wohler — 

"  Your  letters  of  the  5th  and  14th  affect  me  like  a 
story  of  the  old  times ;  there  is  the  old  fire  and  youth, 
and  years  which  are  gone  and  tones  which  have 
sounded  rise  up  and  transport  me  to  the  early  days  of 
our  happy  collaboration.  You  have  kept  your  single- 
mindedness,  and  have  enjoyed  ever-renewed  happi- 
ness ;  but  I  seem  to  myself  like  a  renegade,  a  deserter, 
who  has  given  up  his  religion  and  has  nothing  in 
exchange.  I  have  left  the  paths  of  science,  and,  in 
my  efforts  to  be  of  some  use  to  agriculture  and 
physiology,  I  am  rolling  the  stone  of  Sisyphus, 
which  ever  falls  back  on  my  own  head,  and  I  despair 
sometimes  of  the  possibility  of  getting  it  on  a  firm 
foundation.  .  .  ." 

Again,  in  the  same  year,  he  wrote  : — "  I  admire  you 
and  your  beautiful  researches.  How  happy  you  are 
in  your  province !  You  are  older  than  I,  and  yet  I 
am  much  less  bright  than  you.  Yon  seem  to  me  in 

N 


210  JUSTUS   VON    LIEBIG: 

your  work  like  the  man  in  the  Indian  story,  from 
whose  mouth  bunches  of  roses  fell  whenever  he 
laughed ;  I,  with  the  agriculturists,  am  condemned  by 
fate  to  bear  water  to  the  cask  of  the  Danaids.  All 
I  do  is  in  vain.  I  trouble  myself  and  consume  my 
best  powers  without  gaining  any  result ;  I  have  not 
won  a  single  voice  for  me  and  my  principles  by  the 
Chemical  Letters." 

It  is  needless  to  say  that  these  expressions  were 
but  the  outcome  of  passing  moods,  and  that,  upheld 
by  a  real  inward  conviction,  Liebig  never  ceased  to 
declare  what  he  believed  to  be  the  true  lessons  that 
chemistry  offered  to  agriculture  and  physiology.  Nor 
was  he,  as  time  went  on,  without  abundant  evidence 
that  his  labours  were  appreciated;  for,  besides  the 
ordinary  honours,  which  were  literally  showered  upon 
him,  within  a  single  year  (1865)  a  call  to  Berlin  would 
have  been  his  at  a  word,  he  was  invited  to  visit 
England  at  the  cost  of  Parliament  to  give  evidence 
on  the  utilising  of  town  sewage,  and  received  a  vote 
of  thanks  from  the  Corporation  of  London  for  the 
assistance  he  had  given  in  regard  to  this  difficult 
subject:  though  it  is  to  be  feared  that,  in  this  case, 
he  must  have  been  disappointed  with  the  immediate 
result  of  his  efforts,  for  we  know  he  hoped  that  England, 
with  its  vast  wealth,  was  about  to  set  an  example 
to  the  other  countries  of  Europe,  and  to  teach  them 
how  to  make  use  of  the  vast  stores  of  invaluable  plant- 
food  which,  under  the  name  of  sewage,  is  daily  cast 
irrevocably  away  by  the  great  cities. 

In  1867,  after  much  hesitation,  Liebig  consented 
to  go  to  Paris  as  one  of  the  Presidents  of  the  great 
Exhibition.  In  spite  of  his  hesitation,  this  visit  proved 
a  rich  and  great  joy  to  him,  as  he  told  Wohler 


HIS    LIFE   AND   WORK.  211 

afterwards.  The  renewed  intercourse  with  such 
veterans  as  his  old  friends  Deville,  Fremy,  Wurtz, 
IVligot,  and  Chevreul  was  delightful.  During 
his  visit  he  dined  with  Napoleon,  whom  he  com- 
mended afterwards  as  one  who  "could  not  only 
talk,  but  listen."  In  exercising  his  function  as  a  presi- 
dent, he  was  much  struck  by  the  want  of  order  in 
the  French  committees,  where  the  members  did  not 
address  the  president,  as  in  Germany  and  England, 
but  each  other.  This  made  his  work  difficult  some- 
times, but  his  "  vice  "  helped  him  out,  and  so  he  got  on 
pretty  well.  It  is  interesting  to  notice  that  in  this 
year  Liebig,  for  the  first  time,  dismissed  an  assistant. 
When  he  wrote  at  the  time  to  ask  Wb'hler  to  find 
him  a  new  one  he  paid  a  handsome  compliment  to 
the  pharmacists,  saying  that  he  would  prefer  "  a 
pharmacist,  who  is  accustomed  to  order,  cleanliness, 
and  has  a  sense  of  duty." 

A  large  proportion  of  the  numerous  letters  which 
passed  between  Liebig  and  Wohler,and  of  those  between 
Liebig  and  Berzelius,  have  been  published  since  Lie- 
big's  death — the  former  under  the  editorship  of  the 
late  Professor  Hofmann,  who  was  assisted  by  Frau- 
lein  Emilie  Wb'hler;  the  latter  under  that  of  Justus 
Carriere.  The  earlier  letters  dealt  very  largely  with 
their  scientific  work,  and  will  afford  a  happy  hunting- 
ground  for  future  historians  of  chemistry,  whilst  his 
correspondence  with  Reuning  (1854-73)  will  be  not 
less  interesting  to  agriculturists.  His  later  letters 
to  Wohler,  especially  those  written  from  Munich,  and 
some  of  the  others  were,  however,  much  less  ex- 
clusively scientific.  These  throw  a  clear  beam  of  light, 
by  which  one  gets  some  pleasant  glimpses  of  the 
simple  and  happy  home-lives  of  these  two  men, 


212  JUSTUS   VON   LIEBIG: 

and  of  their  deep  affection  for  each  other.  Very 
many  of  the  quotations  already  given  are  taken 
from  the  letters  of  the  Munich  period.  Individually 
these  letters  are,  most  of  them,  very  simple.  Many 
relate  to  little  gifts  of  bock  or  cigars  from  one  to  the 
other,  or  consist  of  discussions  of  plans  for  holidays, 
or  of  short  descriptions  of  past  excursions,  and  such 
like  matters.  In  one  we  find  Wohler's  daughter 
Fanny  at  Munich  taking  care  of  Liebig,  and  rendering 
"  invaluable"  services  by  helping  him  to  manufacture 
bread  on  chemical  principles.  Several  give  us  little 
domestic  details  of  this  kind.  Thus  one  shows  us 
something  of  the  family  anxiety  for  the  fate  of 
Dr.  Georg  Liebig,  who  was  in  India  during  the 
Mutiny,  but  who  escaped,  and  not  long  afterwards 
came  home,  married,  and  settled  in  the  Fatherland. 
From  another  we  learn  that  all,  or  nearly  all, 
Liebig's  grandchildren  were  the  subjects  of  successful 
experiments  with  his  "infant's  food,"  which  is  still 
often  found  valuable  by  the  doctors.  In  a  few — a 
very  few,  happily — we  hear  of  visits  from  the  Angel 
of  Death.  The  frequent  references  to  his  health  make 
it  clear  that  in  the  later  years  Liebig's  work  was  often 
done  in  the  face  of  great  difficulties.  More  than 
once  his  yearning  for  the  sight  of  his  old  friend's 
presence  shows  itself,  and  we  find  him  giving  voice 
to  the  wish  that  his  few  remaining  years  could  be 
passed  in  Wohler's  company.  Early  in  1861,  when 
he  was  sleeping  badly,  he  wrote :  "  If  only  I  had  the 
old  wish  to  work,  the  old  power  to  overcome 
difficulties  !  Write  to  me  more  often.  Your  chatter 
gives  me  a  cheerful  day.  When  Pfeuffer  comes  to  me, 
he  says  to  me  frequently,  '  Ah,  you  have  had  a  letter 
from  Wohler ! '  " 


HIS   LIFE    AND   WORK.  213 

In  1870  Wohler,  for  the  last  time,  proposed 
a  new  joint  research.  But  Liebig  refused;  he  de- 
clared himself  unequal  to  what  Wohler  proposed. 
"  With  my  last,"  he  says,  "  I  concluded  my  course." 
During  1871  his  health  was  very  poor,  and  it  is  plain 
that  he  then  sometimes  felt  the  end  was  not  very  far 
off.  On  the  last  day  of  this  year  he  wrote  to  Wohler 
the  following  touching  words — 

"  I  cannot  allow  the  year  to  pass  without  a  sign  of 
my  continued  existence,  We  shall  not  for  long  be 
able  to  send  each  other  these  happy  wishes  for  the 
new  year  ;  but  even  when  we  are  dead,  and  have  long 
been  dust,  may  the  bonds  which  have  united  us  ever 
keep  us  both  in  the  remembrance  of  men  as  a  not  too 
frequent  example  of  two  men  who  were  faithful, 
without  envy  and  ill-feelings;  who  wrestled  and 
strove  in  the  same  arena,  and  were  ever  firmly  knit 
in  friendship." 

But  though  Liebig  felt  that  he  must  now  abandon 
the  hope  of  doing  much  more  himself,  his  generous, 
yet  patriotic,  address  to  the  Bavarian  Academy  after 
the  close  of  the  Franco- Prussian  War  shows  us  that 
even  in  1871  he  still  retained  in  a  high  degree  his 
old  vigour  and  fire,  and  that,  if  he  was  sometimes 
saddened  by  the  thought  that  his  own  work  was  so 
nearly  done,  he  was  still  full  of  hope  for  Germany 
and  mankind. 

During  the  winter  of  1872  he  continued  to  lecture 
as  usual ;  in  January,  1873,  he  even  wrote  that  his 
lectures  were  a  refreshment  to  him ;  and  in  the 
following  month  he  was  well  enough  to  be  trying 
experiments  on  the  making  of  cyanogen  and  on  the 
feeding  of  pigs.  But  the  end  was  now  close  at 
hand. 


214  JUSTUS  VON  LIEBIG: 

Liebig's  last  letter  to  Wohler  was  written  on  April 
3rd  of  this  year,  and  the  last  letter  he  received  from 
Wohler  was  written  on  the  7th  day  of  the  same 
month.  Liebig  wrote : 

"  MUNICH,  3rd  April,  1873. 

"  I  intended  to  have  written  to  you  yesterday,  but  I  had  a  bad 
night,  without  any  sleep,  and  the  whole  day  I  lay  tired  and 
exhausted  upon  the  sofa.  I  thought  of  you — your  good  sleep, 
your  good  appetite,  the  normal  activity  of  all  your  functions. 
"Would  it  be  possible  to  perish  in  old  age  merely  through 
sleeplessness,  without  sickness  ?  It  is  the  vegetative  life,  the 
recuperation  in  the  night.  When  this  fails,  the  lamp  is 
gradually  extinguished.  I  was  not  well  a  single  day  in 
Wiesbaden,  and  feared  to  sojourn  in  the  low  ground;  also  many 
other  things  did  not  agree  with  me  there.  I  should  not  be 
averse  to  go  to  Hanau  to  your  brother-in-law.  We  might 
af&rwards  pass  a  few  more  days  in  the  Bavarian  Mountains. 
My  plan  is  to  take  leave  from  Easter  onward,  and  to  do  nothing 
for  the  half  year.  I  have  a  great  wish  to  go  to  Yienna ;  from 
thence  to  Magdeburg,  to  Rimpau ;  then  to  Hamburg  and  Kiel, 
to  Meyer's.  This  is  to  hope  that  you  will  come  with  me.  What 
do  you  say  ?  I  shall  not  go  to  a  cure.  It  was  no  use  to  me  last 
year;  and  in  Wildbad,  for  instance,  walking  through  the  streets 
to  the  bath  is  not  agreeable. 

"  We  have  heard  with  the  greatest  grief  of  the  death  of  your 
sister-in-law  in  Berlin :  she  has  been,  I  hear,  suffering  for  some 
time.  It  is  certainly  my  friend,  General  Hartmaun,  who  is 
dead,  the  same  who  was  with  us  in  Reichenhall.  He  went  to  a 
funeral  in  winter,  and  thence,  as  in  so  many  cases,  contracted 
hi*  fatal  illness. 

"  With  heartiest  greetings  to  Fanny, 

"  Your  faithful 
"  J.  VON  LIEBIG." 

Wohler  was  not  well  enough  to  attempt  to  travel, 
however,  and  on  the  7th  he  replied  as  follows.  This 
was  the  last  letter  he  wrote  to  Liebig : 


HIS    LIFE   AND   WORK.  215 

"  WIESBADEN,  April  7th,  1873. 

"  My  best  thanks  for  your  letter  of  the  3rd.  It  is  now  a  year 
since  we  have  seen  each  other,  and  it  would  distress  me  very 
much  if  it  should  not  come  to  pass  that  we  meet  this  Easter. 
But  I  fear  extremely  that  I  must  resign  myself  to  this.  I  could 
not  come  to  you  this  time,  since  I  have  first  to  consider  the  full 
restoration  of  my  strength,  which  I  hope  to  attain  in  this  mild 
climate  by  a  completely  quiet  life.  I  still  hope  that  you  will 
accept  the  pressing  invitation  of  my  brother-in-law,  and  that  we 
mny  meet  in  Hanau  ;  whereto  your  remark,  '  I  am  not  averse 
to  come  there,'  encourages  me.  You  certainly  seem  inclined 
for  travel,  but  I  am  much  surprised  that  you  wish  to  go  to 
Yieuna,  and  to  rush  into  this  disagreeable,  unsatisf}-ing,  excit- 
ing spectacle,  the  Exhibition. 

"  A  f CAV  days  ago  Buff  with  his  wife  took  us  by  surprise ; 
they  stayed  here  two  nights,  and  then  journeyed  to  Crefeld,  to 
their  son  Henry. 

"  In  answer  to  my  questions,  Lipsius  writes  that  the  eagles  on 
the  captured  French  flags  really  consist  of  gilded  aluminium, 
a  metal  that  was  first  produced  in  Berlin  in  1827.  Sic  erunt 
fata." 

The  visit  to  Hanau  never  took  place.  Liebig  and 
AY <>hler  met  no  more,  for  Liebig  died  at  Munich  on 
April  18th,  1873. 


.  -\^V\MiAA^^r^  ^ 


vi 


INDEX. 


Acids  compounds  of  hydrogen, 
48 

Agricultural  education  and  re- 
search, 124 

Agriculture,  Japanese,  119 

"  ,  Perfect,"  81 

Agriculturists :  Liebig's  desire 
they  should  think  for  them- 
selves, 113 

Air  the  source  of  carbon  for 
vegetables,  91 

,   Relation  of    plants  and 

animals  to,  98 

Alcohol,  Nature  of,  50 

Aldehyde,  Discovery  of,  62 

Ammonium  thiocyanate,  Action 
of  heat  on,  44 

Amygdalin,  Nature  of,  34 

Animal  bodies,  Motion  in,  153 

body,  Motion  of  juices  in, 

155 

—  heat,  131 

Animals  need  nitrogen,  138 

Atomic  theory,  Brief  account 
of,  32,  49 

Autobiography,  10,  12 

Bavarian  Academy,  Address  to, 
198 

Benzoyl,  33 

Berzelius :  description  of  his 
laboratory,  26  ;  electro- 
chemical theory  of,  56 


Bischoff,  Memorial  address  by, 

10 

Bonn,  State  of  science  in,  14 
Boussingault,  Work  of,  86 
Bromine,   Failure   to   discover, 

45 

Carbohydrates,  85 

Carriere  on  Liebig  and  Platen, 

10 

Chemical  equivalents,  49 
Chloral,  Discovery  of,  41 
Chlorinated  vinegar,  59 
Chloroform,  Discovery  of,  41 
Compound  radicles,  33 
Cookery,  Chemistry  of,  160 

Davy,  Lectures  of,  on  agricul- 
ture, 86 

Dualism,  56 

Dumas,  Early  life  of,  51 ;  cor- 
respondence with  Liebig,  51 ; 
and  Boussingault  on  relations 
of  plants  and  animals,  99 ; 
meeting  with  Humboldt,  53 

Early  life  of  Liebig,  1 1 
Education,    Liebig's    influence 

on  methods  of,  173 
English  men  of  science,  Liebig's 

relations  with,  199 
Englishmen,  Memorial  from,  to 

Liebig,  202 


218 


INDEX. 


Enzymes,  78 
Erlangen,  Studies  at,  15 
Erlenmeyer,  Memorial  address 

by,  10 
Ether,  Nature  of,  50 

"  Familiar  Letters  on  Chem- 
istry," 10;  origin  of,  173 

Faraday:  friendship  with  Liebig, 
199 ;  letter  from  Liebig,  200 

Fat,  Production  of,  from  carbo- 
hydrates, 147 

Fermentation,  64 ;  Liebig's 
theory  of,  66 ;  supposed  in- 
fluence of  oxygen  on,  70 ; 
Vitalistic  theory  of,  72 ; 
Pasteur's  work  on,  72 

Ferments,  65 

Food  of  plants,  Source  of,  116 

,  Respiratory,  141 ;  non- 
nitrogenous,  function  of,  144 

Foods,  Classification  of,  141- 
145 ;  plastic,  141 

Formulae,  Method  of  checking, 
159 

Gay-Lussac,  Work  with,  18 
Gerhardt.     Contest     of,     with 

Liebig,  43,  44 

Giessen,  Appointment  to  pro- 
fessorship at,  19;  the  teach- 
ing at,  175 

Glucosides,  Discovery  of,  35 
"  Ground  absorption,"  110 

Hofmann  :  Faraday  lecture,  10 
Humboldt :    kind  assistance  to 
Liebig,  18 


Humus,  88  ;  real  use  of,  98 
Husbandry,   Natural    laws   of, 
113 

Isomerism,  Discovery  of,  29 
Kastncr,  14 

Laboratory,  The  Giessen,  175 
Land,  Deterioration  of,  115 
Lavoisier  on  relations  of  plants 

and  animals,  99 

Liebig  a  pioneer  in  science,  20  ; 
"  Condenser,"  the,  24 ;  and 
Wohler,  friendship  of,  36; 
character  of,  37;  importance 
of  what  he  did  for  physiology, 
152-170  ;  the  first  "  extension 
teacher,"  173 ;  as  a  teacher, 
178;  literary  work,  195; 
memoirs  by,  195;  dominant 
characteristics,  197 ;  and  his 
pupils,  205 ;  last  years,  209 ; 
letters,  211;  last  letter  to 
Wohler,  214  ;  last  letter  from 
Wohler,  215 

Meat,  Extract  of,  163 

extract,  Value  of,  165 

,  Roast,  why  superior  to 

boiled,  162 

Memorial  addresses,  10 

Mineral  manures,  Experiments 
with,  107;  difficulty  of  apply- 
ing, 109 

Minerals  in  plants,  error  con- 
cerning their  origin,  103 

Mirrors,  Silvering  of,  63 


JUSTUS   VON   LIEB1G. 


219 


Molecular  weights,  Methods  of 
finding,  23 

Mulder :  similarity  of  nitro- 
genous components  of  plants 
and  animals,  136 

Munich,  Life  at,  212 

Nitrogenous     constituents     of 

plants  and  animals,  Similarity 

of,  134 

—  foods,  Necessity  of,  138 
Nitrogen,  Sources  of,  for  plants, 

101-106;    elimination  of,  by 

animals,  153 

Oil  of  bitter  almonds,  33 
Organic  analysis,  Method  of,  21 
-   Chemistry,     Export      on 
Present  State  of  (in  1840),  81 

Paris,  Opportunities  for  prac- 
tical study  at,  17  ;  studies  and 
experiences  at,  17;  teaching 
at,  17;  visit  to,  in  1867,  210 

Plants  and  animals,  Relations 
of,  84,  138 

,  Components  of,  100 ; 

produce  the  blood  of  animals, 
135  ;  "accumulation offeree " 
by,  143 ;  their  mineral  com- 
ponents, 107 

Platen  :  references  to  Liebig  as 
a  youth,  15 

Potassium  cyanide,  Method  of 
making,  40 

Reading,  Liebig's  early,  13 
Roscoe,  Obituary  notice  by,  10 


Rotation  of  crops,  Effect  of,  on 
soil,  120 

Scientific   disputes,    Object   of, 

43 

Soup,  163 
Spontaneous  combustion,  Views 

on,  189 
Substitution,  Discovery  of,  58 

Technical  education,  what  it 
means,  185-187 

Tyrol,  Characteristic  adven- 
tures in,  205 

Universities,  German,  How  re- 
search is  taught  at,  177 
Uric  acid,  Investigation  of,  35 

Vegetables  and  animals,  Rela- 
tions of,  84 

Vegetable  tissues,  Components 
of,  85 

Vinegar  plant,  75 

" ,  Quick,  process,"  71 

Vital  force,  167 

Vogel,  Memorial  address  by,  10 

Wander- Year,  14 

Windier,  S.  C.  H.,  letter,  The, 

60 
Wohler,  Early  life  of,  25 ;  and 

Liebig,  meeting  of,  29 ;  and 

Liebig  begin  joint  work,  30 ; 

character  of,  37  ;  letter  from, 

37 ;     work    on    urea,     129 ; 

friendship  with,  in  late  years, 

209 


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